1.52am Update: The returning officer has just announced the result. The Labour majority was 3,558, up from just 103 at the general election, a result that Ed Miliband can cite as evidence that the party is making progress under his leadership.
Elsewhere, as expected, the Conservative vote was badly squeezed – the party's share of the vote fell from 26.4 per cent to just 12.8 per cent. By contrast, the Lib Dem vote actually increased by 0.3 per cent. That will be of some comfort to a party that has recently been as low as 7 per cent in the national opinion polls. The Tories will have more trouble putting a positive gloss on their result. The insistence that the party ran a strong campaign only makes their poor performance appear even worse.
Labour 14,718 – 42.1 per cent (+10.2 per cent)
Liberal Democrats 11,160 – 31.9 per cent (+0.3 per cent)
Conservatives 4,481 – 12.8 per cent (-13.6 per cent)
Ukip 2,029 – 5.8 per cent (+1.9 per cent)
12.25pm We're not expecting an official result from Oldham East for at least another hour but the Lib Dems, most notably the party president, Tim Farron, have already conceded defeat.
Labour is thought to have won with a significantly increased majority, with party officials predicting a majority of between 2,000 and 3,000.
The Lib Dem vote is said to have held up at around 32 per cent, meaning the party has avoided the disastrous possibility of a third-place finish. By contrast, the Tory vote is thought to have fallen sharply and we can expect much criticism of the party's half-hearted campaign to follow. One key issue will be how many Conservative voters have defected to Ukip.
Turnout was 48.06 per cent, down from 61.2 per cent at the general election but still reasonably high for a by-election.
I'll be back when the official result is announced at around 1.30am. For reference purposes, here's how the parties performed at the general election.
Labour 14,186 – 31.9 per cent
Lib Dems 14,083 – 31.6 per cent
Conservatives 11,773 – 26.4 per cent