Chris Huhne said he was kept in the dark about the Tempora spy programme and the British use of the American Prism system despite being a member of both top-level bodies.
The disgraced ex-Liberal Democrat MP said the first he knew of the activities was when documents detailing them were leaked by US whistleblower Edward Snowden to The Guardian.
He also questioned whether the authorities were now seeking stronger legal powers because GCHQ harboured doubts about the present legality of its work or to cover-up past rule breaches.
Foreign Secretary William Hague insists staff acted “in full accordance with our laws and values” and a parliamentary watchdog found it did not use the secret Prism programme to circumvent British law.
Mr Huhne served in the cabinet from May 2010 until February 2012 when he quit to fight allegations he got his then wife to take his speeding points - an offence he later admitted and was jailed for.
“I was also on the National Security Council, attended by ministers and the heads of the secret and security services, GCHQ and the military,” he wrote.
“If anyone should have been briefed on Prism and Tempora, it should have been the NSC.
“I do not know whether the Prime Minister or the Foreign Secretary (who has oversight of GCHQ) were briefed, but the NSC was not.
“This lack of information, and therefore accountability, is a warning that the supervision of our intelligence services needs as much updating as their bugging techniques.”
He said the Snowden revelations left him “shocked and mystified” at why the Home Office had pushed for - and eventually dropped in the face of Lib Dem opposition - stronger monitoring powers.
“Was the Home Office trying to mislead?” he asked.
“Some of the explanations for this political mystery are not pretty.
“Maybe GCHQ is not as confident as it claims about the legality of what it has been doing,” he said - or arranging with Washington to bug each other’s citizens to get around restrictions.”
GCHQ denies being engaged in such “jurisdiction-swapping”.
“Maybe GCHQ is not as capable as its now-leaked boasts claim: every public body has a budget to protect.
“Or it might have been embarrassing, pre-Snowden, to admit to GCHQ’s capability, so maybe the securicrats thought that £1.8bn was a modest price to duplicate what they were already doing.
“I doubt, though, that hard-pressed taxpayers would agree.
“Whatever the explanation, the Home Office was happy to allow the NSC and the Cabinet - along with Parliament - to remain in utter ignorance of Prism/Tempora while deciding on the communications data bill.”