FTSE marks fifth week of gains on China rate cut

* Blue-chip index up 1 pct after surprise China move

* Mining, oil stocks climb

* Salamander up after Ophir's offer to buy peer (Adds closing prices)

By Atul Prakash and Lionel Laurent

LONDON, Nov 21 (Reuters) - Britain's top share index rose on Friday, marking a fifth straight week of gains, after a surprise interest rate cut in China boosted mining and commodities stocks.

Shares (Frankfurt: DI6.F - news) of London-listed miners Anglo American (LSE: AAL.L - news) , Rio Tinto and BHP Billiton (NYSE: BBL - news) were up between 5 and 6.7 percent at 1630 GMT after China's surprise move, seen as a new step in its campaign to support growth in the world's second-largest economy.

The blue-chip FTSE 100 index closed up 1.1 percent at 6,750.76 points. The benchmark index is up about 1.5 percent so far this week and on track for a fifth week of gains in a row.

"In the UK a rising tide lifted all boats with mining stocks being the biggest beneficiaries of rising commodity prices as a result of the Chinese rate cut," Jasper Lawler, analyst at CMC Markets, said.

However, Royal Bank of Scotland (LSE: RBS.L - news) shares fell 0.8 percent after it said it only marginally passed a stress test last month.

Worries over China's economy losing steam, combined with fears of a supply glut, have hit commodity prices and shares. Some warned the rate move was unlikely to change the mining sector's structural issues.

"The oversupply is greater than expected and the speed of reaction from some miners to that has been slower than expected ... The rate cut does not change that," said Nik Stanojevic, analyst at Brewin Dolphin (LSE: BRW.L - news) .

Other energy-related stocks also rose. Tullow Oil (LSE: TLW.L - news) rose 5.8 percent, Royal Dutch Shell (Xetra: R6C1.DE - news) was up 1.3 percent and BG Group (LSE: BG.L - news) gained 2.2 percent. In addition to China's news, prices were helped by the possibility of OPEC deciding on a supply cut next week.

Mid-cap Ophir Energy (Other OTC: OPGYF - news) fell 5.6 percent after the oil and gas explorer offered to buy peer Salamander Energy (Other OTC: SALDF - news) in an all-stock transaction. Salamander shares were up about 0.6 percent.

Outsourcing group Serco fell 5 percent after a downgrade from broker Credit Suisse (NYSE: CS - news) . (Editing by Hugh Lawson)