The WM5140 is getting to be between 5-7 years old, about the age that the carbon brushes in the motor wear out. You can pick up a new set on Ebay for £6.99 including delivery (take a look at item number 131407433619 on eBay). They are pretty easy to change with the motor in situ, though, personally, I like to drop the motor out and do it on the bench.
Is your water coming into the washer clean, is the rinse clean water etc. is it your washing powder are you using enough or putting too many clothes at a time in the washer. And, how long has this been doing this?