Britain's intelligence services had a system of oversight no better than that seen in the TV comedy Yes, Prime Minister, an MP said on Tuesday during a meeting of a Commons committee.

Julian Huppert, a Liberal Democrat, said the sitcom depicting ineffectual government was an appropriate comparison after it emerged that the intelligence services commissioner appearing before MPs worked only part-time, and operated with only one other staff member.

Huppert said: "Can I come back to this comparison between Britain and the US? I presume you are both familiar with Yes, Prime Minister. There is a line there where it says, 'Good Lord, no. Any hint of suspicion, you hold a full inquiry, have a chap straight out for lunch, ask him straight out if there is anything in it and if he says no, you have got to trust a chap's word'."

Other MPs on the home affairs select committee also questioned Sir Mark Waller, the intelligence services commissioner, as to whether there was adequate political and legal oversight of MI5, MI6 and the surveillance agency GCHQ, and suggested the existing system was not robust enough.

Waller, a former judge, had initially refused to attend the committee but had to relent after being summoned. But he told MPs that he thought he had adequate resources to do his job.

Keith Vaz, the committee chairman, said Waller was clearly a "decent man" but questioned whether there was a need for a full-time commissioner, with a bigger staff with more powers.

Waller disagreed, saying that the prospect of a former judge scrutinising applications for warrants was sufficient to ensure that the intelligences agencies behaved properly. He added that he admired the agencies' "ethos" and that a bigger bureaucracy could have a detrimental effect, interfering with the important work of the intelligence agencies.

The intelligence service commissioner oversees the "lawful use of intrusive powers" – surveillance as it is used by the intelligence agencies. Waller also revealed that 1,700 warrants were issued last year. He estimated he checked about 6% of them to ensure they complied with the law.

The committee is investigating counter-terrorism but its hearings have become increasingly dominated by the revelations by the whistleblower Edward Snowden about the extent of mass surveillance and whether there is sufficient political and legal oversight.

Waller had been in the job 18 months when he heard about the Snowden revelations last summer. His response, he said, was: "Crikey."

His initial fear had been that he had been duped by the intelligence agencies. "I wanted to know if I had been spoofed for 18 months," Waller said.

Waller, who looked ill at ease during much of the questioning, said he had gone to see GCHQ to see if there was anything to the allegations. He saw the deputy chief of the GCHQ and was satisfied the allegations were without foundation.

Vaz said: "And how did you satisfy yourself? It seems from your comment that you had a discussion with them."

Waller replied: "Certainly."

Vaz said: "You heard what they had to say."

Waller replied: "Certainly."

Vaz probed further: "And you accepted what they had to say?"

Waller: "Certainly."

"Is that it?" asked Vaz.

"Certainly," replied Waller.

Vaz added: "Just a discussion?"

Waller: "Certainly."

Vaz, in conclusion, said: "And that's the way you were satisfied that there was no circumventing UK law. You went down, you went to see them, you sat round the table, you had a chat?

Waller replied: "You've got to remember that I've done a whole period – a year and a half's inspection. I have got a very good idea as to what the ethos of this agency is. They know perfectly well that they have had to make out their case and the legality of their case, etc, and I have absolutely, clearly, accepted it."

The committee also heard BT has refused to deny it has handed over data on millions of customers in bulk to government agencies, such as GCHQ, a group of MPs has been told.

Big Brother Watch director Nick Pickles told the committee BT had provided "no substantive answer" to the question of whether they had handed over masses of customer data to the UK government.

Pickles told MPs he feared BT was providing data under section 94 of the Telecommunications Act, which gives the secretary of state broad powers to demand information from an individual or organisation in the interests of national security.

Waller was followed on the witness list by Conservative MP David Davis, who has long questioned the extent of surveillance and called for increased political oversight. Asked about the role of Waller and Sir Anthony May, the interception of communications commissioner, who also acts as a watchdog and recently gave evidence to the committee, Davis said: "I think the commissioners are good people doing impossible jobs." Davis called for a beefed-up intelligence committee that was chosen by the Commons.