* FTSE 100 up 0.3 pct; U.S. Fed renews zero rate pledge
* Eyes on Scottish referendum vote; unionists just ahead
* TUI Travel boosted by Morgan Stanley upgrade
* Monitise tumbles as Visa explores options for stake
By Tricia Wright
LONDON, Sept 18 (Reuters) - Britain's top shares rose on Thursday as investors put aside angst about an independence vote that got underway in Scotland to focus on the prospect of an extension of ultra-low interest rates in the United States.
Equities across Europe temporarily trimmed gains when the European Central Bank handed out a below-forecast 82.6 billion euros ($106.38 billion) in its first offering of four-year loans to banks.
But traders said this was offset by expectations that a small figure might prompt the ECB to take more monetary stimulus measures, such as buying assets to print money - a tool known as quantitative easing (QE).
The FTSE 100 was up 21.92 points, or 0.3 percent, at 6,802.82 points by 1101 GMT, propped up by the U.S. Federal Reserve's reiteration on Wednesday of its pledge to keep ultra-low interest rates for a "considerable time".
Scots started voting at 0600 GMT on Thursday and five surveys - from pollsters YouGov, Panelbase, Survation, Opinium and ICM - showed support for independence at 48 percent, compared with 52 percent for the union.
While the UK benchmark clawed itself into positive territory after a weaker start, light volumes exaggerated market moves, with some investors reluctant to place bigger bets until the outcome of the vote was known.
"The markets are starting to price in a win for the 'No's but we're still seeing very low volumes," Mike McCudden, head of derivatives at Interactive Investor, said.
The FTSE 100 had traded just a third of its 90-day daily average mid-way through the trading day.
But in brisk volume, TUI Travel jumped more than 4 percent to the top of the blue-chip leader board after Morgan Stanley upgraded its rating on the stock to "overweight" from "equal-weight" following the tour operator's recent merger agreement with majority owner TUI AG.
Volume in TUI Travel stood at more than double its 90-day daily average volume.
Among other notable movers, small-cap Monitise sank by about 23 percent after Visa Inc said it was exploring options for its 5.5 percent stake in the British mobile banking technology company. Its trading volume was more than three times its 90-day daily average. (1 US dollar = 0.7765 euro) (Additional reporting by Sudip Kar-Gupta)