Twenty years ago the Liberal Party and the SDP united after a long and fraught courtship to form the Liberal Democrats. BBC Parliament tells the story of the protracted marriage negotiations.

A Marriage Made In Portsmouth

With Britain's first-ever political leaders' television debate imminent, award-winning reporter Michael Cockerell uncovers what it's like to take part in these contests and how leaders try to win them. He tells the inside story of why it has taken so long for such debates to arrive in the UK.  The programme features candid interviews with US Presidents and their advisers on the tricks of the debate trade. Blending new film and behind-the-scenes footage, some never seen before, it's a tragicomic tale of high politics and low cunning. From John F Kennedy and Richard Nixon through to Barack Obama, candidates are seen being prepared for their debates, then in the sometimes funny, sometimes disastrous results on live television.  Cockerell shows why for our would-be next Prime Ministers - Gordon Brown, David Cameron and Nick Clegg - the three debate stages across Britain will be what one former US President calls 'Tension City'.