In the mad scramble that ensued in the moments after Gordon Brown finally announced the start of the election campaign, party leaders appeared to head for the nearest mode of transport available as they raced to be the first to meet the public. In fact, each man's movements have been carefully plotted for the next four weeks.

David Cameron's trip to Edgbaston in the Midlands was positively dripping with symbolism. It is a seat he will simply have to win if he is to wrest the keys to No 10 from Mr Brown's grasp. A swing of just over 3 per cent, well within his reach, would be enough to unseat Labour's former health minister Gisela Stuart. The seat was held by the Conservatives for 70 years before 1997.

Mr Cameron's decision to visit the local Queen Elizabeth hospital allowed him to hammer home the message that the NHS would be safe in Tory hands. It will also bring back bad memories for Labour as that's where Tony Blair was ambushed in the 2001 campaign by a member of the public angry that her partner, suffering from cancer, had no bed.

Trudging down the tinned foods aisle of a supermarket in Kent may have seemed like an odd place for Gordon Brown to start his campaign, but his visit to Rochester was intended as a sign that the party is still up for the fight and battling in areas that it is widely expected to lose. While Rochester and Strood is a new constituency with a notional Tory majority of 1,500, the seat it has replaced is Medway, a Labour marginal.

Its retiring MP, Bob Marshall Andrews, prematurely conceded defeat live on television in the constituency in 2001 as he watched votes pile up for the Tories. He eventually held on. By visiting local shoppers and supping tea with constituents, Mr Brown hoped to show he would not concede it so easily in 2010. North Kent was also a region sewn up by New Labour in its pomp.

There is no mystery behind Nick Clegg's decision to head to Watford, Britain's most hotly contested three-way marginal constituency. It has been a popular spot for campaigning politicians and was chosen by William Hague as the launch location for his ill-fated election campaign in 2001. The Liberal Democrats have high hopes of stealing the constituency from Labour. Their candidate, Sal Brinton, earned a huge swing in 2005, beating the Tories into third place. She is standing again and hopes to unseat the junior minister Claire Ward.