Washing Machine

First decide on what type of machine you want. There are plenty of cheap machines out there, but they are cheap for a reason.
Decide on your spin speed, and capacity. The higher the spin speed, the dryer your clothes at the end (although they can tend to crease). If you have out side drying facilites (a line etc) you can go for a lower spin. If you live in a flat, get a higher spin, or even a washer dryer as a last resort.
How many are you washing for? If its a family of four or more, get a big capacity (6kgs+). If its just two or three of you, you can live with a smaller capacity.
Do you want built in or free standing? Built in are a lot more expensive. Do you want brands noted for reliability? Miele and Siemens and AEG, are famed for their reliability. Zanussi is the same gruop as AEG (Electrolux) and Bosch is the same group as Siemens (BSH).
What warranty do you want with it? Siemens and Miele offer five years on some machines, and Bosch offer two years. There is always the option to take out a repair plan or extended warranty.
When do you need delivery? Do you need fitting and the old machine taken away?
Most machines are cold fill only. Don't be worried by this. For an explaination why, go to https://www.washerhelp.co.uk It is a fantastic site written by a very knowledgable person.
Currys and Comet do good headline deals, but always check out your local independant dealers. Their service tends to be better, and price wise, they are usually as good.
Hope this helps.