which, given how close things look now, may mean the result won't be clear until then. Could be a bit of a bummer for the broadcasters - they could go through all the hassle, and then say "we'll be back around midday with the end results".
Constituencies bow to pressure over election counts
Fewer than 5% of counts will now be delayed, the Electoral Commission said.
Up to 25 constituencies are not expected to begin counting until 0900 BST on 7 May, 11 hours after polls close at 2200 BST the previous night.
But with recent opinion polls suggesting the possibility of a hung Parliament - where no single party has an overall majority - this may be sufficient in number to mean the eventual result is not known until late on 7 May.
It has also raised concerns about the security of ballot boxes being held in locations overnight. The BNP have suggested it could lead to vote tampering.
http://news.bbc.co.uk/1/hi/uk_politics/election_2010/8625597.stmThere's a list of the seats expected to be late on the BBc page; I've no idea how many are marginals.
On edit: OK, I compared the BBC list with a list of marginals, and it looks like:
2 Lib Dem held seats the Tories might take (though probably less likely now): Cheltenham, and Westmorland and Lonsdale
3 Labour seats the Tories could take: Copeland, Morecambe and Lunesdale, and Norwich North
1 new seat predicted to be Tory, but might go Lib Dem: Broadland
http://www.electoralcalculus.co.uk/conlist_a_b.html#BroadlandSo I guess it would have to be very close indeed by the end of night-time counting for them not to be able to project a result (plus, I guess, a few knife-edge seats that might need recounts in the morning anyway).