Bahco:
The first thing you should do is get a small black light to locate exactly where the pet stains are.
Most people are unaware of it, but by the time urine starts to smell, it will also fluoresce under ultraviolet light, so you can use a cheap counterfeit bill detector to locate urine stains.
And, that's no bunk either. A very well respected name in the janitorial service sector of the economy is Bane-Clene, and they make a $100 unit specifically for carpet cleaning contractors to locate pet urine stains.
http://www.baneclene.com/catalog/ultra_violet_light.html
But, if you phone around to any of the places listed under "Janitorial Equipment & Supplies" in your phone book you should be able to pick up a professional quality black light for less than that.
Also, your best bet is to phone around to the local carpet cleaning services in your area and ask which brand of carpet cleaning chemicals they like best. They will be buying these chemicals from one of the places listed under "Janitorial Equipment & Supplies" in your phone book. Here in North America it's Ramsey and ChemSpec, but I don't know if those brands are available in Britain. If you can get some concensus on which brand of carpet cleaning chemicals most of the carpet cleaning services in your area like the most, find out which of the Janitorial Supply outlets sell that brand, and buy your cleaning products there.
Now, every place that sells janitorial supplies will also sell direct to the public because none of them will sell to retailers who in turn sell to the public, so there's no one to bark at them for stealing their retail business. The closest thing to a janitorial supply retailer would be a hardware store or grocery store, and they just sell products made for the retail consumer market. Most janitorial supply stores sell to hospitals, school boards, bingo halls, community centers, your local cleaning contractors and other businesses who employ a cleaning crew, but none of them turn around and sell those products to the public, so none of them are gonna get mad if the janitorial supply place sells to you.
The advantage of buying from a Janitorial Supply store that sells to the carpet cleaning professionals in your area is that the staff at that store will also be very knowledgeable about cleaning carpets, and on how best to use the chemicals they sell. That's because they deal with professionals doing this kind of word every day. And, if you buy their chemicals from them, then they'll typically toss in all the technical advice you want or need to do a good job free of charge.
If you don't get any concensus of opinion on who sells good carpet cleaning products in your area, then in the UK, Ring 01293-437511 for Spurgeon, who are Bane-Clene's distributor in Europe. Bane-Clene is a well respected name, and you can't go too far wrong with their products either.
The cleaners you will be buying will be made for professional who typically will have carpet cleaning equipment. However, you can use an inexpensive shop style wet/dry vaccuum cleaner as a carpet shampooer. Just use a spray bottle (or whatever) to apply the cleaner to the stain, and press the end of the suction hose of the wet/dry vaccuum cleaner directly down on the carpet pile to pull out the soiled cleaner. You can't shampoo a whole carpet with a wet/dry vaccuum cleaner, but you can certainly remove stains on a carpet with one.
This web page outlines the products Bane-Clene sells for cleaning pet odors from carpets, and how to use them:
http://www.baneclene.com/articles/pet-odors.html
but, any other company's line of products should also work well for you, so don't be afraid to go with the cleaners that most of the carpet cleaning professionals in your area like most.
In fact, as a landlord I find that MOST of the work I do is cleaning in one form or another, and a good source of reliable information on cleaning can be found here:
http://www.cleanfax.com/index.asp
Cleanfax is the online web site of the Cleaning Management Institute which is a professional society dedicated to the education, training and advancement of the janitorial service sector. The Cleanfax web site seems to be focused a bit more on carpet cleaning than other kinds of cleaning, but I think that might be because there are more specialized kinds of equipment and chemicals for cleaning carpets and upholstery than there are for other kinds of cleaning. Also, there are a lot more training programs for professionals in the carpet cleaning business than in other cleaning businesses.
