BP rally supports Britain's FTSE 100; financials take Swiss hit

* Blue-chip FTSE 100 index flat

* BP top gainer as faces lower oil spill fine, oil rebounds

* Financials under pressure after SNB decision triggers losses (Recasts)

By Alistair Smout

LONDON, Jan 16 (Reuters) - Britain's top share index held steady on Friday, boosted by BP after the oil major received a less than expected fine for the 2010 Gulf of Mexico oil spill.

A rebound in Brent crude helped to support the broader energy sector. However, traders remained cautious heading into the weekend after the Swiss National Bank's surprise decision on Thursday to scrap its cap on the franc saw financials fall in choppy trade.

BP will face a maximum fine of $13.7 billion under a ruling by a U.S. federal magistrate. That was several billion less than anticipated, pushing the stock up 3.6 percent and making it the index's top gainer.

The oil firm added over 10 points to the blue-chip FTSE 100 , which was essentially flat, down 0.04 percent to 6,496.17 points by 1229 GMT after gaining 1.7 percent in the previous session.

The FTSE 350 oil and gas index rose 1.5 percent, the biggest sectoral gainer, as Brent crude oil rose more than $2 to almost $50 a barrel after the West's energy watchdog forecast the market downtrend would end.

The mining sub-index rallied after an early dip to trade 0.7 percent higher as copper gained for a second day.

Financials were the biggest weight on the index, trimming 14 points off the FTSE 100 after the Swiss National Bank's shock decision to end its cap on the franc resulted in big losses for a number of brokers.

Unlisted forex broker Alpari entered insolvency, while mid-cap IG (LSE: IGG.L - news) fell again after being cut to "hold" from "buy" by Canaccord Genuity (Other OTC: CCORF - news) .

It has fallen 5.6 percent in two sessions after saying the SNB's move would hit forecasts by up to 30 million pounds.

"The FTSE is very twitchy after the Swiss announcement on Thursday. People are erring on the side of caution ahead and closing up positions to make sure they're protected over the weekend," Toby Morris, senior trader at CMC Markets, said.

After Thursday's market turmoil, investors are awaiting a European Central Bank policy meeting next week at which the ECB is widely expected to say it will start buying government bonds with new money. Many interpreted the decision to scrap the Swiss franc's three-year-old cap against the euro as a sign the SNB is anticipating just such a tide of euros.

Chartists remained bearish on the benchmark FTSE 100 index, which is down 1.4 percent so far this year after falling 2.7 percent in 2014.

"The downtrend in the FTSE remains intact and... weakness today will push it to its third consecutive weekly decline," Bill McNamara, technical analyst at Charles Stanley (LSE: CAY.L - news) , said. "That's a compelling reason for remaining cautious." (Additional reporting by Atul Prakash; Editing by Mark Trevelyan)