"I still don't believe it happened..."

What's it like to face the most famous clock on television? We chat to Oxford mathematician Dr Tom Crawford - best known as the creator of the award-winning 'Tom Rocks Maths' outreach programme - about what it was like to step into Rachel Riley's shoes on Countdown.

What's the best tactic for tackling the numbers round? How did he prepare? Did he really only have 30 seconds to find a solution? Tom gives us a glimpse behind-the-scenes of this British institution.