His admission that the Government had been ‘economical with the truth’ during its epic battle to ban the MI5 memoir Spycatcher has gone down as one of the most outrageous euphemisms in recent political history.

So it is perhaps not surprising that Lord Armstrong – who was Margaret Thatcher’s Cabinet Secretary for eight years – is now at the centre of accusations of a major Establishment cover-up of child abuse by leading public figures in the 1970s and 1980s.

It has been revealed that he was urged by MI5 to help hush-up abuse allegations against a senior MP so as to avoid political embarrassment for the Thatcher government.

A document from November 1986 shows that Sir Antony Duff, then director-general of MI5, wrote to Armstrong about inquiries into one MP said to have ‘a penchant for small boys’.

Even today, despite years of official investigations into the claims and a top-level review into the loss of hundreds of Home Office files relating to the original allegations, Armstrong defiantly refuses to identify the suspect politician or even say if he is alive or dead. Can he really still believe that it is acceptable to be ‘economical with the truth’?

His attitude reflects an arrogant mindset that has for too long prevailed in Westminster and Whitehall.