In common with all modern washing machines, these will not spin if they have water in them. The catch is that these machines can pump out the water and still not spin because they think that they are still full. This is because the water level control works by air pressure to a diaphragm switch and the system is not depressurising.
The culprit is the white bottle shown in the picture above. It gradually gets choked with muck and goo until the air cannot escape. Removal and thorough cleaning will solve the problem.
After reassembly, you should consider giving the machine a Service Wash at 90˚C and a quality biological powder to clean out the rest of the machine or use a specific cleaner, like Affresh.
As usual, if you intend to do this yourself, ensure that the plug has been pulled.
A Cleaning Product To Solve This Problem
Affresh Washing Machine Cleaner has been specifically developed to combat the problem of smelly or foul smelling washing machine and is available in the online store along with it's sister product Affresh Dishwasher Cleaner.
Is short, Affresh attacks the residue itself, breaking it up and sending it down the drain and, regular use can stop it from happening again. The great thing about this is that it's not stupidly expensive either, it's actually quite cheap.
We get asked all the time on the best way to solve the problem and, especially if it is fairly bad, maintenance washes can take a long time to clear the odours but it still won't remove all the scum that's left, Affresh will as it is specifically designed to break these residues up.