There are no less than 4 variants that fit your machine. To be sure of giving you the correct information, I need the exact model number and serial number (usually on the back).
I would prefer to have someone else come and check out the machine and change the part if possible……can you suggest anyone in the Essex (Witham, CM8) area and an idea of cost ❓
The pressure switch (dependant on version) is between £8 and £15. Labour rates vary across the UK and are best discussed directly with the repairer to be honest.
If you go to repairs@ there are a couple of UK Whitegoods members listed that cover your area 😀