Britain's FTSE heads for biggest weekly drop in a month

* Blue-chip FTSE 100 index down 0.4 pct

* Banks, miners among top decliners

* Focus on Greece's Sunday referendum (Adds PMI data, updates prices)

By Atul Prakash

LONDON, July 3 (Reuters) - Britain's blue-chip share index headed for its biggest weekly drop in a month on Friday, with miners slipping on a slowdown in China and banks falling after Brazil said it was probing some global lenders' currency market activity.

The FTSE 100 was down 0.4 percent at 6,603.64 points by 1117 GMT and hardly moved on data showing Britain's services sector grew more than expected last month.

The index has fallen nearly 2 percent so far this week and stayed on course to record its worst weekly percentage fall since early June on concerns about Greece's debt crisis.

The banking index fell 1.3 percent on news that Barclays (LSE: BARC.L - news) , HSBC, Royal Bank of Scotland (LSE: RBS.L - news) and Standard Chartered (HKSE: 2888.HK - news) , were among those under investigation on suspicion of rigging the Brazilian real.

Royal Bank of Scotland fell 1.9 percent, also hit by news the bank may need to pay $13 billion to settle claims that it misled investors in mortgage-backed securities, according to documents filed in a U.S. court.

The UK mining index fell 1.8 percent after a survey showing services sector activity in China, the world's top metals consumer, slowed to its lowest in five months in June. Rio Tinto (LSE: RIO.L - news) , BHP Billiton (NYSE: BBL - news) and Anglo American (LSE: AAL.L - news) all dropped about 2 percent.

A further sharp sell-off in Chinese stocks also weighed on sentiment. The rout has wiped trillions of dollars off Shanghai- and Shenzhen-listed shares.

"The markets are looking at the bigger picture and focusing on what's happening in Greece and China. The Chinese slowdown and stock market wobbles there are making their presence felt," Commerzbank (Xetra: CBK100 - news) equity strategist Peter Dixon said.

"Investors don't want to be 'long' going into the weekend and would wait for the Greek referendum results for a clearer market direction," he said, referring to a referendum on Sunday that may decide Greece's future in Europe.

The International Monetary Fund delivered a stark warning on Thursday of the huge financial hole facing the country.

An opinion poll published on Friday pointed to a slight lead for supporters of Greece's bailout terms, on 44.8 percent, against 43.4 percent for the "No" vote that the leftwing government backs.

It also showed 74 percent wanted to remain in the euro zone against 15 percent who wanted a "national currency". (Editing by Louise Ireland)