I think everyone would be surprised if the cost of providing security were revealed.
Ministers and ex ministers automatically get it.
I think that it started during the IRA bombing era.
I am personally aware of one particular expensive waste of public money on personal security.
You may recall a local tory who was Home Office minister for a short time, before he got 'lorded' and sent to the Bahamas as governor - can't recall his name - not really top brass risk.
When I was having some redecorating done at Melbourne House (many years ago), the contractor sometimes didn't show some days. I tackled him about it and he explained that he was working on this house in the Ribble valley
, which had been completely rewired with high tec security, and needed total interior redecoration.
Within months the chap was in the Bahamas - what a waste!