LONDON (Reuters) - Britain's top share index slipped on Monday after gaining in the previous five sessions in a row, with outsourcing group Capita (>> Capita PLC) extending its recent losses and precious metals miners tracking a fall in gold prices to 10-month lows.

Capita (>> Capita PLC) fell for a third straight day and closed 5.3 percent lower after a profit warning late last week and its decision to sell its asset management business left analysts questioning the British outsourcing group's strategy.

Russian gold and silver miner Polymetal (>> Polymetal International PLC) slumped 4.7 percent after RBC cut its rating on the stock to "sector perform" from "outperform" and as gold prices slipped to a 10-month low on expectations of a U.S. rate hike this week. [GOL/]

"Polymetal remains an industry-leading precious metals company ... However, with increasing gold price volatility, high levels of 2017 capex and a higher (free-cash flow) break even price than peers we downgrade to Sector Perform," RBC said.

Fellow precious metals miners Randgold (>> Randgold Resources Limited) and Fresnillo (>> Fresnillo Plc) fell 1.4 percent and 3.3 percent respectively.

The blue-chip FTSE 100 <.FTSE> touched a fresh one-month high in early deals, before surrendering gains and closing 0.9 percent lower.

Banks also slipped as some investors took profits after recent sharp gains. The sector index <.FTNMX8350> was down 2.4 percent, dragged down by a 3.3 percent fall in HSBC (>> HSBC Holdings plc) and a 2.4 percent weaker Barclays (>> Barclays PLC).

Losses were capped by a 1.6 percent surge in the oil and gas index <.FTNMX0530> after oil prices rose more than 6 percent to an 18-month high after OPEC and some of its rivals reached their first deal since 2001 to jointly reduce output to try to tackle global oversupply and boost prices. [O/R]

Oil majors Royal Dutch Shell both rose about 1.5 percent.

"The OPEC deal made two weeks ago hinged on the non-OPEC members also agreeing to cut production - many members of OPEC had stated that they would only agree to cut production on the basis the non-members also agreed," said James Hughes, chief market analyst at GKFX.

"The agreement puts the issue of a global oil glut to rest, but only for now."

Shares in Sky (>> SKY PLC) fell 2.8 percent after seeing a record gain of nearly 27 percent on Friday after a $14 billion takeover bid from Twenty-First Century Fox.

The stock pulled back as shareholders and analysts said the offer represented a "low-ball" bid, with one major shareholder set to reject the offer. Fellow broadcaster ITV (>> ITV plc) dropped 3.3 percent.

(Additional reporting by Atul Prakash; Editing by Catherine Evans)

By Alistair Smout