The machine wont spin when in spin cycle and

2 things are possible. Can you tell if the spin cycle is engaging? If the spin cycle is not engaging properly or very fast, then the water will not leave the clothes. less likely is that the machine is not draining the water away properly or fast enough.

Paul, if it has a clutch, yes. If belt drive, check tensioner and replace belt.

Is it a front loader, top loader, what make ? Too many different types and makes to determine the fault. Have you checked to see if the cycle is on drip dry? If it is, the machine wont spin and leaves all the water in the clothes.

Possible blockage in 1 of the outlet pipes causing it to not drain out fast enough and keeping the clothes wet.

sadly its the gear box have it replaced if the machine is old replace the washer as the gear box is a very expensive repair

good luck

this could be due to blockage @pump or the motor wont spin if water not pumped out ..Check filter/clear pump.please leave me me feedback.

Check pump is not jammed or pump / drain filter is not blocked , if so clean /free and re-try , may not require any parts . refer to handbook for location of filter .

a belt has snapped or came off or the motor and brushes are damaged.

Sounds like the machine is not pausing between cycles to allow the transmission to lock into spin.
Eric

It is possible that the belt at the back of the machine is slipping. try running the spin cycle without any load in the machine. I assume this is a front loading machine and you are in UK. the Belt is available on line for about 15 pounds.

If it is running the washing cycles normally, it can't be the motor.