I've used Priceline for a couple of UK trips, thanks to my very British and very tight-fisted boss, and it worked flawlessly. I managed to get rooms in LON and MAN for < £40 per night, which made my boss very happy! The booking worked flawlessly and there were no problems on any of the trips.
The way to get your cheapest room rate is use the "Name Your Own Price" function. Make sure you pick the area you want to stay in at your destination, start at 5 star with a ridiculously low price and make a bid. Then keep either increasing your price or dropping your star rating until you get a hit.
The only draw back is that you have no say in the exact property you stay in and you're immediately locked in. However, I got the Mariott @ MAN airport for £39/n and a decent hotel in West London for the same.
For the UK, try Travelodge - Great value accommodation across the UK and Ireland, as long as you can book well in advance... I've scored London, Manchester and Motorway Services for 29quid a night (with ensuite) or less [there are NO frills like a bar-fridge, free cable/net, air-con nor free muffins for beakfast]. Which has made me very happy!
Last time I used them was Nov 2005. They don't accept Aussie credit cards but I have rellies in the States and used an American card. You can get great deals on hotels but you won't get points for your stay.
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