Normally this comes to £25.73, but Rug Doctor (via branches of Morrisons Supermarkets) are doing a special offer of £19.99 for a 24 hour hire, saving £5.74.
Having looked around, this seems to be a really good deal as for example HSS do a carpet cleaner that is £28.17 for 24 hours and that price doesn't even include any cleaning solution.
You CAN'T book these in advance, it is just a case of going along to a branch of Morrisons to pick one up, might be worth phoning them in advance to check they have one available.
When you pick it up, you need to show proof of ID, ie 1 Utility Bill and Driving Licence.
I've just finished our house and it's quite easy to do and the difference is amazing, really cleans well. The solution provided is enough for all the rooms in our 2 bed house, but I'd recommend you buy more if you have a much bigger place.