Britain’s young conservative prime minister David Cameron has ruled out seeking a third term if he is re-elected, saying it would be “too long” in office.

The 48-year-old was elected in 2010 and is seeking a second term in May, but says he will call time on his leadership after that.

“There definitely comes a time when a fresh pair of eyes or fresh leadership would be good,” Mr Cameron said during an informal BBC interview in his kitchen.

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London mayor Boris Johnson. Photo: Getty

“The third term is not something I’m contemplating.

“I’ve said I’ll stand for a full second term, but I think after that it will be time for new leadership. Terms are like shredded wheat: two are wonderful but three might just be too many.”

British governments are elected for five-year terms.

During the interview, Mr Cameron named several would-be successors to lead the Conservative party, including infamous London mayor Boris Johnson.

According to The Guardian, the PM’s comments have dismayed his party, with a government spokesperson telling the newspaper: “Let’s cross that bridge when we get to it”.

Mr Cameron’s right-wing Conservative party is currently neck-and-neck in polls with the main opposition centre-left Labour party ahead of the May 7 vote.

The Tory leader said he still had a lot more work to do, however, and would be standing for a full second term.

“I feel I’ve got more to bring to this job, the job is half done, the economy’s turned round, the deficit is half down and I want to finish the job.”