8.30pm Update: Sir Peter has just posted the following in the comments below:
"I am interested in your report regarding my retirement as agent for the Huntingdon Conservative Association. You should not read anything into my resignation letter which you have published. My commitment is to the local Party and I will be working towards our success at the forthcoming General Election. However, as I said in my letter to the Chairman, I have health issues which I need to address. Most importantly of all I want to continue my work as a County Councillor representing my constituents in Huntingdon, Alconbury and the Stukeleys. Jonathan is a hard working MP with tremendous support in the constituency. I will work to see the re-election of our local Conservative MP at the forthcoming General Election."
He had been due to retire next year, but has given his association chairman his three months' notice in advance of local MP Jonathan Djanogly addressing a meeting on Thursday to discuss his expenses claims.
Mr Djanogly returned £25,000 he had received in expenses after the Telegraph reported his claims of £4,936 for security gates at his home, and £13,962 and £12,951 for cleaning and gardening respectively over four years. This is the largest amount returned by a Conservative MP (a figure only equalled by Eleanor Laing).
The meeting on Thursday is not a public meeting, as David Cameron has suggested to MPs, but instead is open only to party members and has been described by Mr Djanogly's local paper as a "clear the air" session.
Well-placed sources tell me that that Sir Peter - who is also a member of Cambridgeshire County Council - has been less than happy at the course of events and has not been willing publicly to defend Mr Djanogly's conduct.
In his resignation letter - reproduced below - he pointedly makes no reference to the sitting MP for whom he has acted as agent since 2001: