Carpets get wet, they get mouldy and generally stink......
Current 'trends' in bathrooms are wooden laminate floors.
Homebase do a range which would be suitable for bathrooms.
Bear in mind that traditional floors are at a level suitable to recieve a fitted carpet, so a 'zone' of 10-15mm is normal below doors etc. These laminates are usually around 12m so they will fit ove the floor boards.
Or try B and Q
http://www.diy.com/bq/category/category.jhtml?CATID=159677
http://www.diy.com/bq/category/category.jhtml?CATID=159706
HTH.