The NSA/PRISM scandal has spread to the UK, with the news that American intelligence officials shared telephone and internet data harvested by wiretapping programs with their counterparts at GCHQ (Government Communications Headquarters). According to The Guardian, GCHQ has had access to PRISM data since at least June 2010, and generated 197 intelligence reports from it last year.

Those reports would normally be passed to MI5 and MI6, Britain’s domestic and foreign intelligence services.

The Obama administration has insisted that the PRISM program has not targeted U.S. citizens. However, if foreign citizens of interest were communicating with U.S. citizens, then those Americans would presumably be known to the NSA. Many Americans are skeptical that either their government or the phone and internet companies involved are telling the truth, and with so many questions remaining unanswered, it’s possible that information on American citizens may have been shared with British officials and politicians.

GCHQ has refused to confirm any involvement with the PRISM program, and we don’t, of course, know who in the UK security services would have seen such information. We do, however, know which politicians might have had access to it.

These would include the Home Secretary Theresa May, who is the minister responsible for national security and policing. Also, members of the Parliamentary Intelligence and Security Committee, which has oversight over GCHQ and other branches of the security services.

That committee is chaired by the Conservative MP Malcolm Rifkind, a former foreign secretary and defense minister. The other members are Tory MPs Julian Lewis and Mark Field; Labour MPs George Howarth, Hazel Blears and Paul Goggins; Liberal Democrat MP Menzies Campbell; and two members of the House of Lords: the Conservative peer Lord Lothian, and the unaffiliated peer Lord Butler, a former top civil servant.

It seems clear, meanwhile, that both the NSA and GCHQ have been viewing PRISM data relating to British citizens. If so, the NSA’s involvement is diplomatically embarrassing both for the Obama administration and the British government. GCHQ would appear to have circumvented the usual legal process required for the UK security services to obtain personal information on British citizens from internet and telephone companies.

Demanding that the British government hold an inquiry, Keith Vaz — the Labour chairman of the Commons Home Affairs Committee — said:

I am astonished by these revelations, which could involve the data of thousands of Britons. The most chilling aspect is that ordinary American citizens and potentially British citizens too were apparently unaware that their phone and online interactions could be watched.

If — as Obama and his National Security officials insist — Americans have nothing to be alarmed about, then presumably the involvement of the British security services shouldn’t be an issue either. But the president is a long way from convincing Americans that that is the case.