We are concerned about the lack of oversight by the intelligence and security committee (ISC) regarding the role and function of the NSA at Menwith Hill and other US bases (MPs condemn oversight of spy agencies, 9 May). There is no mention of this secretive and unaccountable US agency anywhere either in the report by the home affairs select committee or in your report and leader (9 May). On 10 April, Fabian Hamilton MP, in a parliamentary question, asked the defence secretary "whether his department was (a) aware of the nature of and (b) consulted before the start of surveillance being carried out at NSA Menwith Hill?" Mark Francois (minister of state, MoD) answered: "Operations at RAF Menwith Hill have always been, and continue to be, carried out with the knowledge and consent of the UK government."

There is a contingence of GCHQ at NSA Menwith Hill. Some of the documents Edward Snowden revealed confirm that unlawful surveillance and intelligence-gathering of vast numbers of citizens was and is carried out in covert programmes at NSA Menwith Hill and with the assistance of GCHQ. The government confirms it has always known about this. The weak and discredited ISC says it has oversight of all US bases. The government sanctions this illegal activity. It's essential that the ISC is scrapped in favour of a meaningful and credible independent committee which has oversight of the activities of the US visiting forces and their agencies as well as GCHQ.

Lindis Percy

Campaign for the Accountability of American Bases

• Malcolm Rifkind accuses Snowden and his supporters of "insidious use of language such as mass surveillance and Orwellian" which "blurs, unforgivably, the distinction between a system that uses the state to protect the people, and one that uses the state to protect itself against the people." Without proper oversight, how would we know?

Barnaby Harris

Buckfastleigh, Devon