Prime Minister David Cameron's approval rating has tumbled to its lowest level since he was elected two years ago, according to a poll on Thursday, after two weeks in which policy gaffes and a funding scandal battered his Conservative Party.

Only 30 percent of voters thought Cameron would make the best prime minister out of the leaders of Britain's three main political parties, the YouGov poll for the Sun newspaper conducted on Tuesday and Wednesday showed.

The figure is the lowest since the May 2010 general election that brought Cameron into power as head of a coalition government with the smaller Liberal Democrat party.

Many have billed the last two weeks as the most damaging for Cameron and his party, after a key fundraiser was secretly taped offering access to the prime minister for cash, and many in the media interpreted last month's annual budget as imposing a Granny Tax on pensioners to pay for tax cuts for the rich.

Mixed messages on how to handle a fuel strike triggered panic and an embarrassing retraction of advice telling drivers to store petrol at home, while a tax on hot food -- including on a snack said to be favoured by the working class -- reinforced accusations that upper class Cameron and his posh inner circle are out of touch with the poor.

Compounding Cameron's problems is a new row this week over plans to boost the state's digital surveillance powers and to hold some trials in secret for national security reasons. The proposals have drawn criticism from members of his own party, the Liberal Democrats and civil liberty groups.

The prime minister may draw some comfort from the fact that opposition Labour party leader Ed Miliband has failed to capitalise on the turbulence, with the number of people who think he would make the best prime minister rising only one point in the last two weeks to 19 percent.

Liberal Democrat leader Nick Clegg's rating is still bumping along rock bottom at five percent, down one point.

Almost half of voters said they did not know who would make the best prime minister, the highest level since the 2010 election, a statistic that may reflect general disappointment with Britain's mainstream parties.

Such sentiment was seen as the driving force behind the shock win last month of maverick leftist George Galloway in a local election in the city of Bradford in northern England.

The YouGov poll weighted its data by age, social class, region, newspaper readership and political party support.

(Reporting by Mohammed Abbas; Editing by Rosalind Russell)