Thanks for all advice.
Parking sensors did not work with no picture on the display.
Tested all sensors individually and none worked.
Garage diagnostic pointed to sensor sounder on the B pillar. Part number 8EO-919-279
This cost £20 through local garage and is on the lower section of the passenger B pillar.
Taking the 2 trim sections off the B pillar reveals the sounder.
I would recommend ordering the two rivets holding the sounder as it is difficult to remove them without damaging them. (Sounder can be taped or glued to pillar if absolutely necessary)
Care is needed to replace the top B pillar trim as it needs feeding into the seat belt height adjuster.
I didn't realise how useful parking sensors were until they didn't work.