Hostilities worsen despite attempts to broker a ceasefire. What happens next requires difficult decisions and hard choices.  
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Russia knows our weaknesses. But do you? 
  
A major five-part series from Sky News and Tortoise which imagines how a Russian attack on the UK could play out – and invites real-life former ministers, military chiefs and other experts to figure out how to defend the country. 
  
Written and presented by Sky News' security and defence editor, Deborah Haynes.