Yet another myth busted..
I guessed I'd always figured HMG collected all kinds of internal stat so they could scope the problem.
Y'know, because being able to measure it's size and growth rate (whatever "it" is) gives you some idea if you can get a tender in from a £1m year business or if you need one of "The Usual Suspects (TM)" and their decades long multi £Bn contracts
But obviously the reason why departments don't know this is because they can't be f**king arsed to collect the data in the first place.
That really does make them astonishingly fu**witted.
Special mention to the Home Office and its role as a designated "Center of Evil" in the British government.