I'm more than happy with a product called Brisk which is from a company called AutoSmart.
They do this as a liquid and a dry foam (the one I use) and all you have to do is spray it over the seats (only a light covering), until it looks like it's snowed on you seats, leave for about a minute the rub with a micro fibre cloth or lightly scrub with a soft brush. Go round the rest of the seats and carpets the same way, once you do this and wiped the dash it should be dry. What it does is lift the dirt from the cloth or carpet.
You can get it from e bay or there will be a AutoSmart rep that works in your part of the UK and they are all mobile, but be warned if you meet the rep don't blame me if you come away spending more and getting more products than you wanted lol.
Two E Bay numbers for you
170483289086
150445995674
If you PM me your post codes where you live I find out who the rep is there.