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Boris Johnson has said he is concerned about how a cap on non-EU immigration will affect London's economy.

The Conservative mayor of London has written to the home secretary to see if rules can be eased for some workers.

The government has pledged to cut net immigration to tens of thousands by introducing a cap from next April.

Mr Johnson, who announced last week he would seek re-election in 2012, also said a cap on housing benefit could force 17,000 families to move.

The cap on non-EU immigration was a Conservative Party manifesto commitment.

Shortly after taking office, Home Secretary Theresa May announced a temporary limit of 24,000 on the number of migrant workers from outside the EU who would be allowed into the UK.

Consultation continues on a final figure for the cap, which may be announced by the end of the year.

But last week it was reported that Mr Johnson had written to Mrs May to say the interim limit on non-EU economic migration was "already causing businesses significant recruitment problems".

He told ´óÏó´«Ã½ One's Andrew Marr Show that London's economy depended on "talent being able to migrate in".

He said there had been a huge "backlash" against immigration due to what he called the previous Labour government's decision to "take the brakes off" - and the cap was the new government's reaction to that.

"It's perfectly reasonable to try and get a grip on it.

"The problem is that this means that, you know, accountancy firms, film firms, banks, lawyers... actually find it very very difficult at the moment to get in some of the people who you really need to keep London's economy going."

He said he had written to Mrs May seeking talks to "see what we can do to address that particular problem - the tier one, tier two applicants who are finding it very difficult to get in at the moment, without taking the brakes off again".

Intra-company transfers - the "tier two" process which allows multinational firms to move their own staff in and out of the UK - were not included in the temporary cap and business leaders have already warned that restrictions could be damaging.

They argue that transfers have no affect on overall migration because the workers either replace someone or leave after completing their contract.

Business Secretary Vince Cable has also said that any restrictions need to be flexible enough to allow companies to conduct their business.

Mr Johnson also said he was concerned about the government's cap on housing benefit - a maximum of £400 a week for a four-bedroom house - announced in the Budget.

He said while he recognised there was a problem with landlords "ripping off" housing benefit claimants, he said in London 17,000 families could be "forced to move" due to the cap.

"I think that's too hard and it would be very difficult to force that in in a prescriptive way," he said, suggesting there should be transitional measures in parts of London, due to the higher cost of housing.

Mr Johnson announced last week he would stand for a second term as mayor of London - Labour's candidates are Ken Livingstone and Oona King.

´óÏó´«Ã½ political correspondent Norman Smith said Mr Johnson was likely to try to take on his fellow Conservatives in the coalition government over cuts ahead of the election and put some distance between himself and Prime Minister David Cameron.