I once looked into using an agency, they wanted a stonking amount per hour and INSISTED on doing a deep clean on the first visit at a extortionate amount. I do not live in a hovel and was not best pleased with this proposal.
Word of mouth is a good way of finding someone I have found.
It's amazing how much a good cleaner can do in a couple of hours. Every week mine dusts and vacs right through, cleans the bathroom, and changes the bedding, does my ironing, cleans all the kitchen surfaces, and washes the kitchen floor. Besides that each week she will do an extra e.g. wash the windows, or clean the oven, or clean the fridge etc..............
There are several companies available that offers best quality cleaning services in affordable price but you should choose the right one to get a best deal. The cost may be between £12 and £15 per hour.
Most cleaning companies require minimum two hours of cleaning on one visit, but offer also laundry, ironing, dish washing. You can get a price around £10 per week
I have reference of a company offering good Stone Cleaning in London so you might check with them regarding your desired services as such they are reasonable only but to be more specific of the budget can choose for a tailor made program.
http://www.fortress-restorations.co.uk