We've only come across 1 job in the last 2 1/2 yrs we couldn't get to with a TM, and that includes Cambridge city centre, flats, etc.
We've talked to traffic wardens in Cambridge, Newmarket & Bury St Edmunds and they all say that as long as we're running hoses from the van to the job they won't issue tickets. We park on double yellows, bike lanes, bus stops, never had a problem.
We kept our porty just in case, and probably won't sell it, but the thought of going back to it.....yeuch.