Factbox: Ten seats to watch on UK election night

(Reuters) - With Britain's parliamentary election on Thursday expected to be the closest run in nearly two decades, the final result might not be clear until most of the 650 seats have declared their winners.

The following are 10 key seats which may give an early clue to the outcome of the election if voting patterns in them are replicated nationwide.

BIRMINGHAM EDGBASTON, RESULT EXPECTED 2345 GMT, MAY 6

This seat was the first gain made by the ruling Labor party in their 1997 landslide election victory. With a swing of just 2 percent needed from Labor, it is likely to be the opposition Conservatives' first gain of the night if they are to win the election.

VALE OF CLWYD, RESULT EXPECTED MIDNIGHT GMT

If the Conservatives win this Welsh seat they will have achieved the 7.1 percent swing needed to win 326 seats and secure an overall majority.

STOURBRIDGE, RESULT EXPECTED 0100 GMT, MAY 7

The 1.5 percent swing toward the Conservatives it would take for Labor to lose this central England seat would mean they will have also lost their overall majority in parliament.

DUDLEY SOUTH, RESULT EXPECTED 0100 GMT, MAY 7

If the Conservatives achieve the 4.5 percent swing needed to take Dudley South in central England from Labor, they will be the largest party in a hung parliament, where no party has overall control.

TORBAY, RESULT EXPECTED 0100 GMT, MAY 7

This is the first Conservative/ Liberal Democrat marginal seat of the night. If the Conservatives do not achieve the 3 percent swing needed to take this seat in southwest England, it may be the first sign that a surge in popularity for the perennially third Lib Dems could dent the Conservatives' prospects.

SHREWSBURY AND ATCHAM, RESULT EXPECTED 0130 GMT, MAY 7

If Labor achieve the 1.8 percent swing needed to gain this seat in western England from the Conservatives, they will have secured an overall majority of 100 seats.

LUTON NORTH, RESULT EXPECTED 0200 GMT, MAY 7

If the Conservatives achieve the 8.2 percent swing required to win Luton North, just north of London, they would have an overall majority of 50 seats in parliament.

LUTON SOUTH, RESULT EXPECTED 0200 GMT

This is a bellwether seat which, since 1951, has been won by the party that goes on to be victorious nationwide. It is currently held by Labor and would require a 7.4 percent swing to the Conservatives if they were to take it, or a 10.1 percent swing for the Liberal Democrats.

MORLEY AND OUTWOOD, RESULT EXPECTED 0200 GMT, MAY 7

While the Conservatives would require a swing of 10.5 percent to take the seat of Schools Minister Ed Balls, one of Prime Minister Gordon Brown's closest confidents, they have made the northern England constituency a specific target.

The defeat of someone as high profile as Balls would be symbolic for the opposition party, who hope to create a "Portillo" moment reminiscent of when then Conservative Defense Minister Michael Portillo lost his seat in 1997, despite going in to the election with a large majority.

EDINBURGH SOUTH WEST, RESULT EXPECTED 0300 GMT, MAY 7

The seat of Finance Minister Alistair Darling is considered to be one of the most vulnerable of any cabinet minister.

While the swing to from Labor is not expected to be as great in Scotland, Darling could lose his seat if the Conservatives achieve a uniform swing greater than 8.2 percent.

* Swing percentages are based on those compiled by Professors Colin Rallings and Michael Thrasher from the University of Plymouth, and have been rounded to one decimal place.

(Compiled by Kylie MacLellan)