(Adds latest probabilities)
LONDON, June 14 (Reuters) - The implied probability of a British vote to stay in the European Union fell to 62 percent on Tuesday from about 78 percent last week, according to betting odds from Betfair.
Bookmakers, who up until last week had the "In" camp as the strong favourite, have cut the odds on a British exit, or Brexit, after polling firms indicated growing momentum for the "Out" camp ahead of the June 23 membership referendum.
According to Betfair odds, the implied probability of an In vote stood at 62 percent at 1220 GMT after earlier falling to as low as 55 percent.
As recently as last Thursday, betting odds had indicated a 78 percent probability of an In vote, according to Betfair, and markets have taken fright in recent days.
Bookmaker William Hill said it was now likely that the "Out" campaign would become the favourite in EU referendum betting by the weekend, if the trend continued.
"We were forced to shorten our Brexit odds yet again overnight ... and the momentum is such that it seems inevitable Brexit will be favourite by the weekend if this trend continues," said Graham Sharpe, William Hill (Other OTC: WIMHF - news) 's spokesman.
(Reporting by Kate Holton; editing by Stephen Addison)