MI6 chief John Scarlett's agency said it has had to prioritise its work

Parliament's Intelligence and Security Committee (ISC) said that extra funding for the services may be needed.

The head of MI6, John Scarlett, told the committee that counter-terrorism accounted for more than half of his security service's workload.

The government said the scale of the terrorist threat meant some of the work had been "reduced but not overlooked".

'Maintain capabilities'

The ISC's annual report said 200 extremist networks were currently under investigation.

We believe consideration may need to be given to separate, additional funding Intelligence and Security Committee

In evidence, MI6 told the committee - which monitors the work of the security services - that it had "not had any choice but to prioritise" this area.

The report said: "We are concerned that aspects of key intelligence and security work are suffering as a consequence of the focus on counter-terrorism priorities.

"We believe consideration may need to be given to separate, additional funding to maintain the agencies' capabilities in these areas."

In response, the government said: "Resources are finite and it is necessary, given the scale of the threat from international terrorism and the unique role of the agencies in countering the threat, that work on some other intelligence and security requirements has been reduced.

"But they have not been overlooked."

Cabinet reshuffle

The report also expressed concern about the disruption caused by last summer's floods to the government's Cheltenham monitoring base, GCHQ.

Meanwhile, former foreign secretary Margaret Beckett has been chosen as the new chairman of the committee.

Mrs Beckett replaces fellow Labour MP Paul Murphy - who was made Wales secretary in Gordon Brown's recent cabinet reshuffle - as its head.

Mrs Beckett left the cabinet after Mr Brown became prime minister last summer.

The ISC is made up of senior MPs and peers chosen by the government.