The coalition is braced for a rough ride tonight as counting gets under way in key local elections.

Polls closed at 10pm amid speculation that a drizzly day across much of the country could result in a low turnout.

The Tories and Liberal Democrats are expected to lose hundreds of the around 5,000 seats at stake on 181 local councils across England, Scotland and Wales.

But Prime Minister David Cameron will be hoping that Boris Johnson can buck the trend by securing re-election as London Mayor.

An eve-of-poll survey for the Evening Standard suggested that Mr Johnson - who gave a confident thumbs-up as he arrived to cast his ballot in north London this morning - is set for victory over Labour's Ken Livingstone, by a margin of 53 per cent to 47 per cent.

A senior Labour source said early signs were that the party had performed "strongly".

They expressed confidence about gains in the Midlands and South, including key battlegrounds such as Harlow and Reading.

Mr Cameron and Labour leader Ed Miliband were early visitors to polling stations in London this morning, accompanied by their wives Samantha and Justine, while Lib Dem leader Nick Clegg cast his ballot alone in Sheffield, as his Spanish wife Miriam does not have a vote.

Recent opinion polls have shown a clear national lead for Labour - often in double digits - as the Government has wrestled with a month-long string of difficulties.

Respected election experts Colin Rallings and Michael Thrasher of Plymouth University say Labour's advantage should translate into a dramatic gain of as many as 700 seats.

That number was seized on by Tory Communities Secretary Eric Pickles who said Labour could reach the target "just by turning up" as he attempted to minimise the impact of any heavy defeat.

Most of the contested seats were last up for grabs in 2008 - when the Conservatives made significant gains and Labour and the Lib Dems were hit hard.

In turn, Labour tried to downplay expectations, suggesting its hope was for between 300 to 350 gains in England and 100 in Wales - with continued losses to the SNP in Scotland.

Sources have stressed Mr Livingstone's "underdog" status, saying that if he wins it will be due to a wider resurgence for the party.

The Lib Dems are braced for a second consecutive year of losses, though they hope to avoid a repeat of the hammering they suffered last year and do not fear coming fourth behind Ukip.

Some 10 cities are also holding referendums on whether to have elected mayors. The idea is expected to get a lukewarm response, despite enthusiastic backing from Mr Cameron, who yesterday said he would like to see "a Boris in every city".