Hi, a gremlin has reared its head. My reverse sensors occasionally beep constantly as if I am up against something when reverse is selected. The noise will continue for a short while after driving off. I was also told my reverse lights do not always come on, I think when the sensor issue is there. Am I correct in thinking it may be an intermittent fault on the reverse switch itself?

The system does indeed stay live for a short while after driving off sir...

Morning, if there is an issue with the reverse light switch it is a separate issue from the sensors giving a constant tone. When selecting reverse, apart from the obvious, it will merely make the PDC system live. If there is nothing withing range of the sensors you won't hear anything. If there's a problem with the reverse switch not operating when engaging reverse it simply won't activate the PDC system.
If the PDC system is giving a constant tone as if you're hard up against an obstacle but there's nothing there, check to make sure none of the sensors have been slightly pushed in, and that there's no dirt on them. You will have also noticed the front and rears have a different pitch tone, so is it the fronts that seem to be activating of the rears?
And as been already said, the PDC will remain live after driving off until you reach around 10MPH.

Agree as in above posts, sounds like you have two problems, intermittent reversing switch fault as you say sometimes the reversing lamps do not come on, and a fault on the sensors.

Believe it or not corrosion on the surface of the sensor will cause a problem similar to what you are experiencing. I had similar and simply emery papered the surface of the sensors and repainted them. Problem solved and not returned for a good few years.

Thanks all. I will start by checking the sensors as previously described on here. Then take it one thing at a time.