By Michael Taylor
LONDON, April 17 (Reuters) - The FTSE 100 <
> of Britain's leading shares reversed earlier gains by midday on Thursday, down 0.3 percent as beaten-down banks led the upside but weakness in oil stocks weighed.At 1120 GMT the blue-chip index was down 18.4 points at 6,027.8 to track back from a two-day winning streak but remain above the psychological 6,000 mark.
Oil shares were weaker as crude prices <CLc1> eased after hitting a new high of $115 a barrel. Royal Dutch Shell <RDSb.L> dipped 1 percent, BP <BP.L> shed 0.4 percent, and Cairn Energy <CNE.L> dipped 2 percent.
Traders said there was a feeling among investors that the price of oil was peaking.
Banks extended gains however, on hopes that an intervention plan being considered by British authorities will help ease tensions in the mortgage market, with lender Alliance & Leicester <ALLL.L> up 3.9 percent and HBOS <HBOS.L> rising 3 percent.
A Treasury source said earlier that British authorities could announce details of the plan, which is expected to allow banks to temporarily swap mortgage-backed securities for government bonds, as early as next week.
Barclays <BARC.L>, Royal Bank of Scotland and Lloyds TSB <LLOY.L> advanced 2.1-2.8 percent.
"The business I'm seeing is on the short side...a lot of uncertainty out there," said Matt Basi, a sales trader at IG Index. "Slightly surprised we didn't see more of a boost today (in banks) -- it sounds like good news for people looking for liquidity."
"Perhaps giving banks a touch of a lift but there is general uncertainty out there and a feeling that any short-term measure might be delaying the inevitable. Light volumes on the long side."
The FTSE 100 slipped out of positive territory after first-quarter earnings from Merrill Lynch <MER.N>. The world's largest brokerage reported a first quarter loss, after taking several billion dollars of writedowns for subprime mortgages and other risky assets.
Further on the downside, Vodafone <VOD.L> slipped 0.7 percent after the Financial Times said the mobile phone giant was considering joining the bidding for Tiscali <TIS.MI> as the Italian telecommunications group set a deadline of May 5 for initial non-binding offers.
Also, Nokia Oyj <NOK1V.HE>, the world's biggest maker of mobile phones, said it expected the cellphone market to fall in euro terms in 2008.
Weighing on sentiment, British housebuilder Taylor Wimpey Plc <TW.L> lost 4.7 percent after it said that based on current market conditions in Britain and the United States its 2008 results will be at the lower end of its expectations.
British shopping catalogue and educational supplier Findel <FDL.L> dived 38.2 percent after it issued a profit warning as it made a higher-than-expected provision for bad debts due to the credit crisis, sending its shares down over 30 percent.
SABMILLER RAISES SOME CHEER
Shares in SABMiller <SAB.L> tacked on 4.6 percent to 1,172 pence and a near three month high, after Lehman Brothers raised its price target on the global brewer to 1,290 pence from 1,265 pence with an "equal weight" rating.
Miners headed south as metal prices dipped following large gains on Wednesday, with BHP Billiton <BLT.L>, Anglo American <AAL.L>, Kazakhmys <KAZ.L> and Vednata <VED.L> between 0.2 and 1.3 percent lower.
Rio Tinto <RIO.L>, which is fighting a takeover from BHP, was down 1.1 percent after it said it was about a quarter of the way through a plan to sell $10 billion in assets this year to offset some of the $39 billion it paid for Canadian aluminium maker Alcan.
Shares in Thomson Reuters, formed by Thomson Corp's more than $16 billion cash and stock purchase of Reuters Group Plc, debuted at 1,700 pence and traded down at 1,644 pence ahead of dealings starting later in the day in Toronto.
ABN AMRO began coverage of Thomson Reuters with a "sell" rating and a 1,500 pence price target.
(Additional reporting by Dominic Lau; editing by Elaine Hardcastle)