Long-term net migration to Britain has risen to a record high, official data showed on Thursday, underscoring the challenge David Cameron has on his hands to convince voters that his immigration policy will work.

Cameron is under pressure to deliver on a promise made in 2010 to reduce annual net migration to Britain to below 100,000. The pledge was aimed at assuaging voter concerns about the strain being placed on public services.

But data from the Office for National Statistics (ONS) showed a net 330,000 people moved to Britain in the year ending March 2015, compared to 236,000 in the same period a year ago.

The ONS said the number surpassed the previous record of 320,000 seen in the year ending June 2005.

The quarterly figures have become a regular source of political embarrassment for Cameron who has insisted he is still working towards the 100,000 target.

Growing levels of immigration have long been a sensitive issue for some Britons, fuelling support for the UK Independence Party (UKIP) which wants to sever ties with the European Union and impose much tighter immigration rules.

Cameron, who was elected for a second term in May, has been criticised for setting a fixed target for migration because, as a member of the EU, Britain is unable to prevent migrants from within the bloc moving to the country to work.

The data showed a net 183,000 people came to Britain from within the EU, up by 53,000 from the previous year.

Cameron's centre-right Conservative Party has sought to clamp down on migration by tightening visa rules and it wants to make it harder for migrants from within the EU to access Britain's welfare system.

Many employers say the attempts to slow immigration will make it harder for them to find the skilled workers they need.

"Scrabbling around to find measures to hit a bizarre and unachievable migration target is no way to give British businesses the stable environment they need," saidSimon Walker, director general of business lobby group the Institute of Directors.

The group has, along with think tank British Future, called for a review of Britain's immigration policy.

Reforms to curb the attractiveness of Britain for migrants are one of the key aims of Cameron's bid to renegotiate Britain's ties to the EU before he puts the country's continued membership to a public vote by the end of 2017.