Yeah long beep is the sensors faulty alert.

Yup, its got a white box and a black speaker unit next to it.

So I guess at some point the car has had reverse sensors installed, ah well mystery solved then :) will remove that at some point as there is no actual sensors in the bumper...

I think you can just unplug it from the loom where it is, might as well leave it there just incase you ever feel the need to refit sensors.

A couple of weeks ago, my sensor gave me the dreaded long beep. Once selected revserse, it gave the standard short beep but then this was followed by a continuous long beep. This was an indication of a fault. I washed the bumper as it was quite dirty and everything worked as normal again.

As above, if you select reverse and get a long beep of about 10 sec, it is a warning that a fault is detected in the system and the system will not work. For the rest of the time the ignition is on the system will not work when every reverse is selected. When the car is keyed off and then back on again the system does a new check when reverse is selected for the first time, and if a fault is detected again, the long beep is sounded, etc etc.

What you can do it is put the car in reverse with the ignition on, but engine off. Got a listen to each of the reverse sensors. They should click continuously. The ones that don't are the ones that have caused the fault. So check the wiring or swap the sensors with the ones that do click and see if the fault moves. that way you can work out if the sensor is faulty, or the wiring is faulty