The coalition Government is braced for a kicking amid signs of a strong Labour performance in local polls.
The party made early gains from the Tories in key town Basildon, as well as securing seats in Great Yarmouth and Southampton. Meanwhile, the Liberal Democrats were looking at losses in Sunderland, Lincolnshire and Manchester.
However, there were rumours that the Labour leader of Bradford council, Ian Greenwood, had been defeated by a Respect candidate. George Galloway pulled off a shock victory in a by-election for the parliamentary seat in March.
A senior Labour source hailed victory in Harlow as a "significant breakthrough", saying that the party had to win the constituency at the general election 2015 to gain a majority.
The result "shows people who used to vote Labour returning", according to the source.
Party organisers in Birmingham were "very confident" they had taken control of the key target, and looked set for success in Newport.
But Tories stressed low turnouts in areas such as Dudley, suggesting it could have dropped to 28% from nearly 37% in 2007.
Party figures also hit out at "apathy" in mayoral referendums, saying turnout in one Nottingham ward was just 8.4%.