Would a nearer and cheaper option be somewhere like Berrybrook/New Elms/Williams?
Is this an intermittent fault, or is it now persistent (which would be much easier to debug). Are you sure there is 12V across the pump when the fault is present (which would suggest an earth problem somewhere i.e the currenty from the pump is not gettinhg back to the negative battery terminal)?
https://jvsautoelectrical.co.uk/ is a Southampton mobile electrician (but I have no experience if they are good or bad, or indeed mobile)
Is it perhaps worth reaching out to the local MSCC noggin and seeing if there is an electrical expert there? (
https://www.logmog.co.uk/)
Sorry, can't be much help I'm afraid....
