I have just had James Evans of “Parking Sensors Hampshire” visit and replace the Parking sensor system in my Mk3.5 that was defective.
An execellent job and included spraying the new sensors the right colour to match the car in just 1.25 hours for £160 all in 
James covers Reading, Hamsphire, Sussex, Newbury & Dorset and also fits fully gauranted Camera systems also.
http://www.reversepark.co.uk/#:~:text=We%20fit%20parking%20sensors%20and,%2C%20Reading%2C%20Newbury%20and%20Winchester.