In the 20 years since it was popularised, “not fit for purpose” has become an a universal by-word for state incompetence, something bureaucrats and their ministerial bosses reach for when they are trying to strike a tough, no-nonsense tone.

The Hansard record of parliamentary proceedings suggests it has been used nearly 3,000 times in the Commons and Lords since 2006. In the 20 years before that, the phrase was used just 37 times.

It has been deployed in debates ranging from conditions in armed forces housing to the sewerage system of a Cornish hospital.

In our interview with him, Sir David wanted to clear up some myths that have become attached to the term.

It was originally a reference to the Immigration and Nationality Directorate, a unit within the Home Office, rather than the entire Home Office.

And it was a description of technology, management and processes in the unit and not the whole staff or the immigration rules.

To be fair to Lord Reid, he made those distinctions at the time but his caveats have been lost in Whitehall lore.

Proving that words can go on hurting for decades, the phrase was dismissed on Newscast as “dismissive and “generic” by Lord Reid’s immediate predecessor as Labour home secretary, Charles Clarke, who returned to the backbenches following the 2006 foreign prisoners debacle.

“Obviously, as in any organisation, there are things that are done well and things that are done badly,” Clarke told us.

“And the job of the leadership… is to review how the department is doing, where it’s doing badly, where it’s going well, and what you have to do to rectify or learn from those things.”

Nonetheless, those four little words – not fit for purpose – were followed by large consequences.

Prime Minister Tony Blair transferred responsibility for prisons from the Home Office to a new Ministry of Justice (MOJ).

The MOJ and its agencies now employ 90,000 staff, making it the largest government department, according to the Institute for Government think tank.

And “not fit for purpose” has become the phrase of choice for reforming politicians.