Checking the wikipedia article on the Mountbatten, I found a link to Ken Livingstone describing the history in parliament, including his policy recomendations:

House of Commons Hansard Debates for 10 Jan 1996 (pt 43)

Mr. Livingstone: Madam Deputy Speaker, I am pointing out that treason against Labour Governments has been endemic in MI5 throughout its history, and that it has co-operated with Conservative Members of Parliament against the elected Government of the day. On those grounds, and because I do not believe that Stella Rimington or anybody else has done anything to change the climate of treason in the organisation, I oppose the Bill. I believe that MI5 should be broken up, and any worthwhile bits of it given to the police to operate as usefully as they can within the law.

I agree, not only about MI5 but in general about secret services.

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