An array of Freedom of Information requests have produced some interesting results for the BBC Radio 4 programme The Political Club on the cost and number of the political class in the UK. According the programme: "For the UK's 22,737 councillors and their assistants, the bill for pay and allowances was £241.5m."
There has been lots of attention on this site and elsewhere to councillors allowances. Rather less to the practice of employing full time assistants to councillors. The information the BBC got hold of was that Councils are employing 108 political assistants at a cost of £2.94 million. But the BBC regard this as a "quite significant underestimate." Councils have defined the term as narrowly as possible in their replies to the FOI requests.
It also only concerned with those assistants in a party political role. It would not include scrutiny coordinators, press officers, those assisting councillors with case work, etc, etc.