Mitie Share News (MTO)

* Winton's David Harding among those backing 'In'

* Crispin Odey, Paul Marshall advocating 'Leave'

* Funds bearish on pound, but no clear Brexit positions

By Simon Jessop, Maiya Keidan and William James

LONDON, May 19 (Reuters) - Are some of Britain's largesthedge fund managers putting their money where their mouth is onBrexit?

That question is causing some disquiet following theintervention of several top hedge fund figures in the debateover whether Britain should vote to leave the European Union.

Most of Mayfair's money managers, many of whom don't evenadvertise the names of their funds on their discreet town househeadquarters in London's West End, usually keep a low profilewhen it comes to politics.

Yet they have taken an uncharacteristically public stand onBrexit, with several flagging their voting intentions in thehope of persuading undecided Britons as the June 23 referendumon EU membership nears.

Appeals from the likes of David Harding of Winton Capital,John Armitage of Egerton Capital and Crispin Odey of Odey AssetManagement have added extra weight, with generous donations tothe campaigns on either side of the debate.

But to what extent are these hedge fund heavyweights alsotaking trading positions on the outcome?

"They should set out how they are positioned," HelenGoodman, a Labour lawmaker who sits on parliament's influentialTreasury Select Committee, told Reuters.

"The public should know who's putting money into thedifferent campaigns and why they might be doing that - becausethat will inform their view of the literature and informationthey get," Goodman added.

While some hedge fund managers have donated to politicalparties in the past, their engagement in this campaign isnoticeably higher than either at last year's general election or2014's Scottish independence ballot.

But while large hedge fund investors are privy to a fund'spositions through regular communications, these details are onlyoccasionally reported and few funds are willing to revealwhether the rhetoric of their leaders is reflected in theirtrading positions.

A Reuters survey of 32 British managers resulted in justthree identifying a Brexit-specific bet, with the rest decliningto specify how they were positioned as the information was notpublic and could negatively impact returns.

Data from the CFTC, however, shows aggregate hedge fund betsthat the pound will fall against the dollar - a Brexit isexpected to push sterling lower - are near a four-year high.

While official polls are still too close to call, bettingodds on Thursday indicated the highest chance to date of Britainvoting to stay in the EU, with the chances of a win for 'in' putas high as 83 percent.

THE SHORT OF IT

Electoral Commission data released last week shows Winton'sHarding, founder of the $30 billion systematic trading firm, asthe biggest campaign donor in recent months with a 750,000 pound($1.1 million) gift.

The Electoral Commission declined to comment on hedge funddonations to the referendum campaigns.

Harding says his "remain" stance has nothing to do with hisfund's trading positions and is critical of rivals who may havesomething to gain from a vote to leave, arguing that hedge fundsare better off with Britain inside the EU.

"The romantic vision of Brexit might bring short-term gainsto some hedge funds, but building a big business for the longterm is easier in a bigger market," he told Reuters.

On the other side of the argument is Savvas Savouri, apartner at $4 billion firm Toscafund, whose managers have arange of trading positions likely to change in value dependingon the outcome.

However, Savouri says his stance is based on an economicview that Britain has more to gain from trading withfaster-growing non-EU economies than with the bloc.

"There are nations around the world that dwarf the EU," hetold Reuters.

Veteran investor Odey, who also favours Brexit, has shortpositions - bets that stock prices will fall - on severalBritish companies, although he declined to comment whether thevote was an influence on these trades.

Odey had 16 open 'short' positions above 0.5 percent of thetarget firm's stock, the level requiring regulatory disclosure,at May 18, but eight were recently scaled back, regulatory datashowed.

A fund's long positions - bets a share price will rise -need to be disclosed when they hit 3 percent of a target firm'sstock and every percent above that, but there is no requirementfor regulators to aggregate that information.

Marshall Wace, co-founded by Brexit supporter Paul Marshall,had 15 outstanding short bets on British stocks above thethreshold and had added to 11 recently, filings showed. The funddeclined to comment on its trading positions.

Several hedge fund managers told Reuters that the outcome ofthe vote is too uncertain for them to take positions aimed atmaking a profit from it, with one Brexit-supporting creditmanager dismissing the idea of trading the outcome as"fanciful".

"We think we know where our risks lie with regard to Brexitand we manage those risks, but it's not a fundamental trade wehave on," the London-based manager said.($1 = 0.6913 pounds) (Additional reporting by Guy Faulconbridge; Editing by SineadCruise and Alexander Smith)