Ok I think you will find its going to be worn carbon brushes in the motor causing this fault.
What you need to do is remove the back panel and take the motor out from the bottom.
Then look at the back of the motor and you will see the carbon brushes. Take them out and see if they have worn down. If so then you need to replace them and that should cure the fault for you.
As when you get this fault were it doesn't spin with a load if you empty it and run it empty as theres no strain on the motor it will turn for a bit but will stop again.
So check them and replace them and this should cure the fault and get it up and running again.
If you need anymore info just get back to me.
OK - thanks - I'll give that a whirl.
No worries let me know how it goes.
Excellent. Splashed out £5 on a pair of replacement brushes including delivery ( probably could of got them cheaper but .. ). Slapped them in and ... hey presto - all working again.
It also runs smoother too. It was starting to vibrate a bit. Don't know if that is coincidence or not.
Cheap simple fix - just what I like.