MILAN (Reuters) - British shares steadied on Thursday as investors sought fresh catalysts after a run that lifted the country's main indexes to record highs, while Petrofac (>> Petrofac Limited) saw one third of its value wiped out amid worries over a fraud investigation.

Data showing that Britain's economy slowed more than previously thought in the first three months of 2017 pushed sterling lower, while the FTSE - which benefits from a weaker currency - recovered slightly from earlier lows.

The FTSE 100 <.FTSE> ended up 0.04 percent, shy of a record high hit last week, as weakness among commodity stocks was more than offset by stronger financials and consumer stocks.

The biggest stock movers were mid caps, although the FTSE 250 <.FTMC> index also ended broadly unchanged and very close to the record high hit this week.

Petrofac fell 30 percent, making it the biggest FTSE 250 faller, after the oilfield services firm suspended its chief operating officer in response to a British investigation into alleged bribery, corruption and money laundering.

Investors feared the investigation and the suspension of COO Marwan Chedid could hurt the company's ability to win work.

"We are concerned that (Chedid's) departure may have a knock-on effect on Petrofac's operational oversight and ability to secure new work," Morgan Stanley analyst Robert Pulleyn said.

Another top faller was Tanzania-focused miner Acacia Mining (>> Acacia Mining PLC). Its stock was under pressure for a second day, down 12.8 percent, after the country's mining minister was fired on Wednesday following an investigation into possible undeclared exports by miners to evade tax.

"Acacia has been accused of under-reporting contained gold in concentrate ... This is highly unusual but we see this placing its licence to operate under pressure," RBC analysts said.

They downgraded the stock to underperform citing uncertainty around future implications, but noted how a resolution was still possible, creating "a value opportunity".

Elsewhere the focus was on an Organization of the Petroleum Exporting Countries meeting in Vienna, which decided to extend cuts in oil output by nine months to March 2018 in a bid to drain a global glut that has depressed markets.

The decision had little impact on equities but sent oil prices sharply lower, dragging down the energy sector and making it the biggest weight on the FTSE.

"OPEC members had a chance today but bottled it. A nine-month extension just isn't enough to really lift oil prices as we'll continue to see US shale fill the gap," said Neil Wilson, analyst at ETX Capital in London.

Oil major BP (>> BP plc) fell 1.1 percent on the back of falling crude prices.

Among other commodity stocks, miners Anglo American (>> Anglo American plc), Rio Tinto (>> Rio Tinto plc) and Glencore (>> Glencore PLC) all fell but came off lows as copper prices reversed course to hit three-week highs as worries about prolonged disruptions at the giant Grasberg copper mine in Indonesia triggered short-covering.

Among top FTSE gainers was 3I Group (>> 3i Group plc), which rose 3.7 percent after a broker lifted the price target on the private equity and venture capital company.

Intermediate Capital Group (>> Intermediate Capital Group plc) soared 14 percent after its full-year results, and GVC Holdings (>> GVC Holdings PLC) rose by 2percent after a first-quarter update.

Media group Daily Mail and General Trust (>> Daily Mail and General Trust plc) fell 6.8 percent as it warned that revenue in its information business would be lower than previously forecast after posting a fall in first half profit.

(Editing by Gareth Jones)

By Danilo Masoni