The security service MI5 forecast that the stability of the British state could be severely threatened by a developing economic crisis and the growing militancy of the left during the 1970s, according to documents released to the public today.

In the final days of the Wilson era, MI5 drafted a contingency paper based on a scenario in which a Labour government, acceding to trade union and other militant demands, radicalised its policies against the private sector and the UK's Nato commitments.