I think all washer dryers use a condenser dryer.
Tumble Dryers come in vented and condensing variety. Vented ones require a 4inch hole in an outside wall to blow the hot moist air outside. Condensing ones pass the hot moist air over cold plates to get rid of the moisture and then discharge the remaining warmish dry air into the room. Condensing tumble dryers need somewhere to get rid of the water. They either collect it in a tank which you need to empty or if they're sited close to a waste outlet they can discharge the water straight into that.
As for washer dryers, since the washing machine part of them requires a waste outlet the dryers they fit to then are always of the condensing variety as they can use the same waste outlet to get rid of water when they're on a drying cycle.
Co-Op electrical shop are pretty good. I've used them a lot and they allow you to pick the delivery day when you order on most items
http://www.coopelectricalshop.co.uk/...oupCode=LDWDRY
If you want some more specific advice it might be worth a look at the forums
here. They're normally a very helpful bunch.
Word of warning though don't buy a cheap washer dryer as they're one of the least reliable white goods you can buy. I suspect you'll find the Bosch one is about the cheapest they'd recommend