For decades the Security Service did not officially exist. Now it posts on Instagram. But what is MI5? How has it transformed itself since the second world war? And what kind of people work there? Ros Taylor speaks to former Guardian security editor Richard Norton-Taylor and a former legal director of MI5, David Bickford.

Richard Norton-Taylor is the former security editor of the Guardian and the author of several books including The State of Secrecy: Spies and the Media in Britain, and David Bickford, a former legal director of MI5 and MI6 and thriller author – you can get his latest, Cold Protocol, for £5 using the code on his website.

The standard history of MI5 is The Defence of the Realm: The Authorised History of MI5 by Christopher Andrew, which is very long and currently available cheaply on Kindle. Not everyone rated it. Stella Rimington published her autobiography Open Secret, and Eliza Manningham-Buller wrote Securing Freedom.

I also drew on an article by H Dylan, The Intelligence Lobby Before the Intelligence Lobby: MI5 Director General Stella Rimington and the Hunt for the New Legitimacy, Rimington's 1994 Richard Dimbleby lecture and MI5 director Ken McCallum's 2025 threat update,

The account of Anthony Blunt's confession can be found at the National Archives, as can the booklet on Observation.

Margaret Thatcher's Commons statement about Blunt, Tony Blair's response to the 7/7 bombings and footage of the Bishopsgate IRA bombing are available online.

The Imperial War Museum North's exhibition on spies is on until August.

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Dynamic, dreary – Britain has 2,300 miles of motorways, and the country would grind to a halt without these tarmac arteries. But they were part of a fast, futuristic post-war vision. Will we ever build another one?

Ros Taylor talks to Chris Marshall, who runs roads.org.uk, and the musician and comedy writer Jason Hazeley. You can find a special MJT motorway playlist on Spotify, compiled by Jason, Ros, producer David Turnbull and listeners.

Readings are by David Turnbull . Ernest Davies, MP for Enfield, spoke about the need for motorways in 1957 and R Gresham Cooke (Twickenham) discussed speed limits in 1958.

I drew on Motorways (James Drake, H L Yeadon and D I Evans, Faber & Faber, 1969), On Roads (Joe Moran, Profile Books, 2009) and Always a Welcome - the glove compartment history of the motorway service area (David Lawrence, Between Books).

The Motorway Archive contains a vast amount of detail.

The National Express 'Elaine' and Trusthouse Forte ads are on YouTube. The BBC broadcast a documentary in 1969 on The Cost of Motorways. Egon Ronay's service station reviews are available here.

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Britain was one of the last countries to go decimal – and had Margaret Thatcher not abolished the Metrication Board, we might have abandoned miles and pints too. Ros Taylor finds out how Britons were persuaded of the merits of getting rid of shillings and farthings, and why the revolution went unfinished.

Mark Stocker is an art historian who works with the Museum of New Zealand (Te Papa Tongarewa) and is the author of When Britain Went Decimal: The Coinage of 1971.

Warwick Cairns is the author of About The Size of It: The Common Sense Approach to Measuring Things.

Seth Thévoz voiced a Commons speech by the MP for Horsham, Peter Hordern, in 1970. He also read an extract from a Guardian article by Anthony Burgess, Damned Dots (1966) which is not available online.

Sir John Wrottesley's intervention in 1824 and the riposte can be read here.

The BBC's Decimal Day 1971, Nationwide, ITV's Granny Gets the Point, the Royal Mint history of decimalisation and a Thames TV report on metrication were useful sources. Max Bygraves' Decimalisation is on YouTube. Your Guide to Decimal Money, circulated to all households, can be read online. A 1975 Conservative memo discussing metrication is at the Margaret Thatcher Archive. I also drew on Andrew J Cook's PhD thesis, Britain's Other D-Day: The Politics of Decimalisation (University of Huddersfield, 2020).

The UK Metric Association and Metrication UK campaign to complete the metrication revolution.

"Ask a man whether women should wear slacks and the answer is almost certain to be a firm 'No.'" How did women get to wear the trousers? Ros Taylor talks to fashion expert Belinda Naylor and Purna Sen, who wore trousers to her sixth form in 1978 – and was thrown out.

Belinda Naylor is a producer with an MA in fashion curation. Her Instagram, where you can find some of her favourite women in trousers, is @fashion_chatter.

Purna Sen is the former head of human rights at the Commonwealth Secretariat and a visiting professor at London Metropolitan University.

The extract from the Manchester Guardian in 1952 is voiced by Seth Thévoz.

The clip from The Seven Year Itch starring Marilyn Monroe is available on YouTube.

Man Alive: The Office Christmas Party (1970) is also on YouTube.

In 2002 the Guardian explained why schools could still choose whether to impose skirts. I also drew on Amy Gower's doctoral thesis, Schoolgirls, identity and agency in England: 1970-2004, University of Reading, 2021.

Lego has pictures of its early minifigures.

In 1948 Britain declared an Emergency in Malaya

It wasn't really an emergency. It was a guerrilla war.

And Britain would spend 12 years trying to drive communists out of its territory. What were we doing there?

Ros Taylor talks to Open University history professor Karl Hack and Economist bureau chief Dominic Ziegler about what the UK did in Malaya, and why Singapore cultivates positive memories of British occupation.

The Imperial War Museum's exhibition Emergency Exits: The Fight for Independence in Malaya, Kenya and Cyprus is on until 26 March.

Karl Hack is Professor of Asian and Imperial History at the Open University. He is the author of The Malayan Emergency: Revolution and counterinsurgency at the end of empire (Cambridge University Press).

Dominic Ziegler is the Singapore bureau chief at The Economist. Faris Joraimi's writing is here.

Footage of Australian soldiers in Malaya comes from a public relations film at the Australian War Memorial YouTube channel.

Lee Kuan Yew's 1989 speech on immigration is on YouTube.

Seth Thévoz voiced James Griffiths, secretary for the colonies, Anthony Eden (both in 1951) and Ernest Popplewell, the MP for Newcastle-upon-Tyne, in 1952. All three speeches are in Hansard.

Singapore's Heritage Trail tells the story of the second world war there. Freedom House publishes an annual report on Singapore. The British Army Review ran a special edition on the Malayan Emergency in 2018.

'Oh, bugger orf!' We all know Received Pronunciation when we hear it. But what makes this accent distinctive? Why do people still pay to learn how to speak RP – and does it really bring the advantages it used to?

Ros Taylor talks to voice coach and actor Alix Dunmore and Professor of Phonetics Jane Setter about how to spot an RP speaker – and how the accent has changed over the past century.

Speeches by Lord Brabazon of Tara and Lord Wedgwood are taken from a Lords debate in 1943 and are voiced by historian Seth Thévoz.

Alix Dunmore runs Alix Dunmore Accent Coaching.

Jane Setter is Professor of Phonetics at the University of Reading. She is the author of Your Voice Speaks Volumes: It's not what you say but how you say it, the Cambridge Handbook of Phonetics and the Oxford Handbook of Language and Prejudice, as well as co-editor of the Cambridge English Pronouncing Dictionary.

Queen Elizabeth II's 1957 Christmas speech is available at the Royal Family YouTube channel. Prince William' interview is here. 1943 BBC Archive audio is on Facebook, as is Daniel Craig reverting to Scouse. The BBC has investigated how Queen Elizabeth's accent changed during her reign. Stephen Fry, an RP speaker, hosted an entertaining episode of Fry's English Delight about spoken English.

No one dies of diphtheria or polio in Britain any more. Since World War Two, we've virtually wiped out the diseases that used to kill tens of thousands of children every year. But rolling out a vaccine isn't always easy.

Ros Taylor talks to public health historian Gareth Millward and Stuart Blume, the author of Immunisation, about jabs and why some people refuse them.

Gareth Millward is an Assistant Professor at the University of Southern Denmark in Odense and the author of Vaccinating Britain: Mass vaccination and the public since the Second World War.

Stuart Blume is an Emeritus Professor at the University of Amsterdam and the author of Immunization: How Vaccines Became Controversial.

Diphtheria Immunisation and Big Whoop are on YouTube. Surprise Attack is at the Wellcome Collection. Polio Diagnosis and Management is at the BFI.

I also drew on the National Library of Medicine, the Science Museum and the Office for National Statistics.

It's built for cars. The buses are baffling. But it's got the most energy efficient housing in Britain. What did it take to build a city from almost nothing? And a university where there are no students on campus?

With architectural historian John Grindrod, Ros Taylor tells the story of Milton Keynes and the Open University.

With thanks to John Grindrod, the author of Iconicon, Concretopia and Outskirts and the presenter of Monstrosities Mon Amour. His forthcoming book, Tales of the Suburbs, on LGBTQ people in suburbia, is out in February 2026.

Seth Thévoz read Lords speeches by Baron Richard Mitchison and Lord Gerald Gardiner, both in Hansard.

Milton Keynes: Shopping as it Should Be and an ITN report from 1967 are available on YouTube. Clips of Harold Wilson and Jennie Lee are at the Open University Digital Archive, which explains the OU's founding. This was an invaluable source of OU history. I also drew on the vast resources at the Milton Keynes Living Archive and the original Plan for Milton Keynes.

It was silly. It was addictive. For decades, millions of kids would gaze at the same people and laugh at the same jokes at the same time. How did children's TV shape their minds? And what will it look like in a world of unlimited digital content?

Ros Taylor talks to Anna Home, who joined the BBC in the 1950s, and screenwriters Chitro Soundar and Angela Salt.

Anna Home was an English TV producer and executive and is the chair of the Children's Media Foundation. She is the author of Into the Box of Delights: A History of Children's Television.

Chitra Soundar is the author of Nikhil & Jay and a writer for children's books, TV and theatre.

Angela Salt is a screenwriter for international children's TV.

Herbert Morrison was speaking in the Commons in 1952 about the BBC charter.

The BFI and the Science and Media Museum have useful resources on early kids' TV. This is the first episode of Play School. Episodes of Grange Hill, Jackanory, Basil Brush, Thunderbirds and many other series are available on YouTube. The BBC interviewed people about Grange Hill in 1980.

More Jam Tomorrow is taking a two-episode break. We'll be back in less than a month, on 28th August.

In the meantime, I have one big ask.

Please let me know if you would support a fifth series of Jam.

Just go to morejamtomorrow.com and hit the link at the top of the page that says "Have Your Say on Series 5." Or just click here: https://tally.so/r/wv85Xd

See you on 28th August, when we'll be back with episode eight.