* Data watchdog says investigating number of data requests
* But says UK intelligence agencies are acting lawfully
By Andrew Osborn
LONDON, April 8 (Reuters) - Britain's law enforcement and intelligence agencies may be overusing authorisations to access private communications data, the official who regulates the activity said on Tuesday, declaring he had begun an investigation into the matter.
Interception of communications commissioner Anthony May said he had also studied concerns raised by former U.S. intelligence operative Edward Snowden about Britain's GCHQ eavesdropping agency and cooperation with the U.S. National Security Agency. But he found no evidence of "indiscriminate mass intrusion".
May said in a report that there had been over half a million occasions last year when various government agencies had been allowed to access details of people's phone calls and emails.
"It seems to me to be a very large number. It has the feel of being too many," May, a peer and a senior judge, said in his report, passed to Prime Minister David Cameron and parliament.
"My office is in the process of undertaking an inquiry into whether there might be an institutional overuse of authorisations to acquire communications data," he added.
A spokesman for Britain's Home Office (interior ministry) said May's review was welcome, but stressed communications data was a vital in serious and organised crime investigations.
"Communications data has played a significant role in every major security service counter terrorist operation over the last decade and is used in 95 percent of all serious and organised crime investigations," the spokesman said.
Snowden's accusations against the NSA and Britain's GCHQ, which were widely publicised in the British media, embarrassed Cameron and raised fears that ordinary Britons were being routinely subjected to unwarranted mass surveillance.
May concluded Britain's interception agencies did not conduct indiscriminate mass intrusion or have the "slightest interest" in screening innocent people's communications data.
"British intelligence agencies do not circumvent domestic oversight regimes by receiving from U.S. agencies intercept material about British citizens which could not lawfully be acquired by intercept in the UK," said May.
Cameron said he thought thought the report brought welcome clarity to what he called "a number of public concerns and myths that have developed in the light of media allegations linked to Edward Snowden."
In 2013, May said there had been 2,760 interception warrants issued, 19 percent fewer than the previous year.
Despite his concerns about the number of communications data requests, he said the number of authorisations for such data in 2013 (514,608) was lower than 2012 when there had been 570,135.
Police and law enforcement agencies had accounted for most of the authorisations, he said, while 11.5 percent had been granted to the intelligence agencies. (Editing by Ralph Boulton)