* FTSE 100 up 7.61 points at 6,445.11
* BP lifted by Macondo-related legal reprieve
* Aviva rises after US sale raises more than expected
* Tesco rebounds as Citi ups rating
By David Brett
LONDON, Oct 3 (Reuters) - The FTSE 100 rose late on Thursday, boosted by heavyweight BP which won a rare legal battle related to its oil spill in the Gulf of Mexico, but ongoing U.S. government shutdown uncertainty sapped momentum.
Energy firm BP - the UK's fifth biggest company by market capitalisation - rose 1.2 percent after it won a legal reprieve in a settlement related to the 2010 Gulf of Mexico oil spill, potentially sparing it billions of dollars of extra costs.
More broadly the FTSE 100 was up 7.61 points at 6,445.11, by 1445 GMT, outperforming all other European peers which were in negative territory.
"The FTSE 100 has underperformed other European indices in the last week such as the CAC and DAX, so there may be some catching up (to do) as there are still a number of companies, which are on low price-to-earnings ratios and offer plenty of recovery potential," Ronnie Chopra, a strategist at TradeNext, said.
One such company Chopra mentioned was Aviva, which gained 1.3 percent after the sale of its U.S. unit fetched $800 million more than expected.
Tesco rebounded 2.2 percent and was one of the most heavily traded stocks after Wednesday's report of a plunge in profits prompted big falls in that day's session.
Traders said that an upgrade to the stock by Citi to "neutral" from "sell" was helping to counteract downgrades from elsewhere.
"There were very few points of light in Tesco's results... so why upgrade now? Simply stated, we fail to see much misperception about the company," analysts at Citi said in a note.
Household goods producer Unilever and drugmaker GlaxoSmithKline, both of which have suffered sharp falls recently, also rallied, rising 1.9 and 1.5 percent, respectively.
The broader market, however, remains stuck in a 200-point range since the start of August.
More recently equity markets have been capped by the budget deadlock that has shut parts of the U.S. federal government and there was no breakthrough in negotiations on Wednesday.
"At the moment there is no incentive to make investment decisions given the backdrop," Keith Bowman, analyst at Hargreaves Lansdown, said.
"Investors are trying hard not to become flustered and panicked by what is happening in the background but is there really any incentive to make new investments?"
The index has back-tracked since hitting 13-year highs in May and is 5.6 percent off that level as investors wait for corporate earnings, which are still in downgrade territory, to catch up with the index's re-rating. The FTSE 100 trades on a 12-month forward price-to-earnings ratio around 13 times, above its 10-year average.
"We went below 6,400 and bounced from yesterday's lows, and since then we've had rising lows, which is good to see," Mike van Dulken, head of research at Accendo Markets, said.
"But for a breakout, we need to get back towards 6,520 ... (The index is) still under pressure, and we might stay in a range until we get something major from the U.S. to get sentiment going again." (Reporting by David Brett; Editing by Christina Fincher)