Isn't First Past the Post wonderful? No? No. However, there is a nice bonus for the people of Sedgefield. They have the power to unseat the Prime Minister, and (for Labour voters) to do it without handing a seat to the Tories. There is a strong independent in Reg Keys.
Rory Bremner writes on this issue, saying:
If all Conservative voters in Sedgefield, and Lib Dem voters, and disillusioned Labour voters, vote for Keys, it could be enough to overturn his 17,000 majority. It's possible.
According to the homepage, the polls show Blair and Keys neck in neck! However, this would be a massive result, given that in 2001, Tony got over 60% of the local vote. Unfortunately I have been unable to find an independent poll to back this up. I'd love to see one!
For balance: Michael Howard is standing in Folkestone and Hythe. Based on the 2001 results, Labour voters there wishing to 'decapitate' the Tories should vote Lib Dem. Charles Kennedy is in Ross & Skye, in 2001 he polled roughly 3 times the votes of his nearest rival, the other parties all got very similar votes. Like Tony Blair his seat seems safe, unlike Tony Blair there is no obvious protest available (something which itself is another argument for making votes count).
A list of other candidates can be found here.
Additional: There is the cleverly named Blair Ditch Project