LONDON: British Prime Minister David Cameron's Conservatives have notched up a four point lead over the opposition Labour Party ahead of a May 7 election, an Ashcroft poll showed on Monday, the party's largest lead in the polling series in six weeks.

If replicated across the country in the election, the lead would not be enough to give the Conservatives an overall majority, however, and was within the margin of error. A week ago, the same poll had both parties neck-and-neck.

The closeness of the race was underlined by two earlier polls on Monday, one of which had the Conservatives two points ahead while the other had the same lead for Labour.

With no sign yet of a surge in support for either the Conservatives or Labour, polls indicate that a hung parliament is the most likely outcome, potentially handing the role of king maker to the leader of a smaller party, such as the Scottish National Party or Liberal Democrats.

Monday's poll, funded by Michael Ashcroft, a former deputy chairman of the Conservatives, put Cameron's party on 34 per cent, up 1 point since last week, and Labour down 3 on 30 percent.

Support for the United Kingdom Independence party (UKIP) was unchanged on 13 per cent, while the Liberal Democrats were up 1 point on 10 per cent.

Pollsters have said the Conservatives would need a lead over Labour of 7-9 points to secure an overall majority of 326 seats, while Labour - because of the way constituencies are divided up - would need to be around 3 points ahead, assuming a uniform swing across the country and no change for the other parties.