We've had a couple of different cleaners and the good ones have always been the ones that were recommended, either by friends or work colleagues. They were usually fairly small companies.

We had friends in London who had had a recommendation for a cleaner from their friends... everyone in their local group of friends had the same cleaners. One weekend the whole group of friends went for a weekend away together and the cleaners cleaned out each and every one of their houses! So check them out yourself,even if they do come highly recommended!

My DH is travelling a lot with work so he would randomly show up while they were there, seemed to keep them on their toes!