LONDON (Reuters) - The Bank of England's new Financial Policy Committee may have to take unpopular action to limit future credit bubbles in Britain, and should resist calls to directly stimulate lending, one of its members said in an interview.

Under legislation about to make its way through parliament, the FPC will sit at the apex of Britain's post-crisis system of financial regulation from next year, keeping an eye out for system-wide threats - so-called macro-prudential regulation.

FPC member Alastair Clark - who has spent much of his career at the Bank and the finance ministry - said it could be an uphill struggle for the FPC to find support and credibility.

"It will be hard work. I think it makes more important that the objective - and what is, and what isn't, in it - is made clear," he told Reuters.

The FPC last week called for powers to set maximum leverage ratios for British banks, set extra capital requirements for riskier lending, and require them to vary their capital buffers to smooth out the swings of the credit cycle.

This choice of powers has already drawn criticism from some politicians and banks. Andrew Tyrie, an influential MP in the Conservative party, has said the FPC should be more willing to stimulate lending as well as to rein it in.

And the chief executive of Standard Chartered, Peter Sands, damned the body as "simultaneously extremely interventionist and extraordinarily blinkered" in an opinion piece for the Financial Times newspaper.

In Clark's view, safeguarding financial stability meant identifying and tackling problems in the financial system which, if left unchecked, could trigger a future crisis, as well as ensuring banks were prepared for another crisis when it came.

Unlike the Monetary Policy Committee, which seeks to avoid undershoots as well as overshoots of its 2 percent inflation goal, the idea of a symmetric target did not translate easily into macro-prudential policy, he said.

"You need to have some process that ensures you don't systematically overcook things in a restrictive direction. But it's a more difficult proposition ... if you mean deliberately leaning in the opposite direction," he said.

Concerns about slow credit growth in the aftermath of the this financial crisis or future ones would be better addressed by government or monetary policy, he added.

"I would have a very real question about whether the FPC has available to it the instruments to give a deliberate push to credit," he said.

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Clark said excessive caution had been a major reason why past financial regulation had failed to stop the crisis.

"People wanted a high degree of certainty and by the time there was a high degree of certainty it was too late," he said. "We have got to try and shift that by taking action earlier and more decisively, even though it may be recognised that in some circumstances it will turn out to be unnecessary."

The fact that macro-prudential policy is subject to greater uncertainty and longer timeframes than monetary policy also needs to be accepted by politicians, Clark said.

"There has to be a political will to accept that actions will be taken which are unpopular and could even turn out to be unnecessary, but they were the best judgement at the time."

The FPC surprised many observers last week by not asking for powers to set maximum loan-to-value ratios in Britain's mortgage market, as is already done in economies like Hong Kong which have some form of macro-prudential policy.

But Clark rejected criticism that a reluctance by the FPC to take actions that would hit homebuyers directly was a bad omen in terms of its future resolve.

"The argument that it is a bit 'wet' not to do this is a little bit facile," he said. "In political circles there has to be an acknowledgement that it is legitimate for the FPC to make decisions in that area without it constantly becoming a political football."

Moreover, as research into the area developed, the FPC was likely to ask for more powers - if not this year or next, then certainly in less than five years, Clark said.

The FPC will also continue to monitor the structure of Britain's financial system, an area of particular concern to Bank Governor Meryvn King, who chairs the FPC and is worried about banks that are too big to fail.

"It could be in many ways more important than some of the more short-term conjunctural stuff. I hope that FPC will give time to thinking about that," Clark said.

Amid the uncertainty about the FPC's tasks, at least one thing was clear for Clark - that it will take a long time to know whether it is a success.

"Come back in 25 years and I'll tell you if it's delivered," he said.

(Editing by Catherine Evans)