* Sterling eases from 3-week highs vs dollar and euro
* Pound implied volatilities fall
* Markets look to Yellen's testimony (Updates prices, adds comments)
By Hideyuki Sano and Masayuki Kitano
TOKYO/SINGAPORE, June 21 (Reuters) - The British pound eased against the dollar on Tuesday, a day after posting its biggest daily gain in 7 years on the back of opinion polls that swung in favour of the campaign for Britain to stay in the European Union.
Two opinion polls on Monday showed that the "Remain" camp has recovered some ground in Britain's European Union referendum debate. implied probability of a "Remain" vote in Thursday's referendum rose to around 78 percent after falling as low as 60 percent last Thursday, according to odds from gaming website Betfair. For the latest Reuters news on the referendum including full multimedia coverage, click British pound GBP=D4 eased 0.1 percent in Asian trade to $1.4658, having pulled back from a three-week high of $1.4721 set on Monday. It rose 2.1 percent on Monday, its biggest daily gain since late 2008.
"The market is reacting to every twist in opinion polls but trading is becoming choppy because people are avoiding taking big positions ahead of the poll. Our options desk was fairly quiet yesterday," said Kyosuke Suzuki, director of forex at Societe Generale (PA:SOGN).
"Polls seem to suggest support for 'Remain' is rising, but the truth is we won't now until we see the results," he said.
This is the third time the currency pair has tested the $1.47-48 band since May and a clear break of those levels could spark a wave of short-covering in the pound.
But traders also said any break may have to wait until the markets see the results of Thursday's referendum.
"Until then, there could be more ups and downs," said Masashi Murata, currency strategist for Brown Brothers Harriman in Tokyo.
The latest swing in opinion polls in favour of the "Remain" camp also adds to the risk of an especially sharp market reaction if the actual vote result, expected to reach markets on Friday morning in Asia, were to go the other way, Murata added.
"As a risk, we have to be on guard on the Tokyo morning of June 24... It could lead to a pretty serious situation if the result turns out to be 'Leave'," he said.
The implied volatility on pound options have fallen notably as investors see a diminishing chance of the "Leave" camp winning. The three-month volatility last stood at 13.3 percent GBP3MO= , compared with a high of 18.5 percent last week.
The euro rose 0.5 percent against sterling to 77.31 pence EURGBP=D4 , regaining a bit of ground after setting a near three-week low of 76.925 pence EURGBP=D4 on Monday.
Against the dollar, the euro EUR= edged up 0.1 percent to $1.1326 EUR= .
The dollar index =USD .DXY stood at 93.582, holding above a one-month low of 93.425 hit earlier this month, as the market awaited U.S. Federal Reserve Chair Janet Yellen's testimony before the Senate Banking Committee at 10 a.m. local time (1400 GMT).
The dollar edged up 0.1 percent to 104.01 yen JPY= . Earlier on Tuesday, the dollar slipped to 103.58 yen, bringing the yen close to its 22-month high of 103.555 set last Thursday.
"At the root of the yen's strength lie diminishing yield gaps between Japan and the U.S. Since expectations of further easing in Japan have waned, Japanese exporters' bids tend to support the yen," said Koichi Yoshikawa, executive director of finance at Standard Chartered (LON:STAN) Bank.
After the yen's latest rise, Japanese Finance Minister Taro Aso said on Tuesday that Japan would respond to rapid currency moves in line with G7/G20 agreements, although the country would not intervene in the market so "easily". dollar briefly fell from around 104.10 yen to 103.85 yen or so after Aso's comments, but later stabilised.
(Editing by Sam Holmes)