Could be multiple things
As you say the height sensor looks like it needs changing, the pressure is too low I believe for the tank, could be a the pressure switch common fault but that usually gives another error code.
On the front height sensor have you checked the wiring? Common problem again and you can get a loom repair kit for it.

Does the compressor cut out at all, or does the pressure in the reservoir change?

Wouldn't suggest springs ideally, will kill the value of the car! 

yeah certainly could be pal , im at work now but hope to get a full day on it tomorrow so will check wiring harness while looking at fitting the new sensor , I take it I can just support the car and remove the wheel ? its on the bump stops already and I couldn't find a WIKI the deals with height sensor changes

Yeah it's a bit off a ball ache to jack up in a normal jack, I always leave a door open or disconnect the battery, just to stop it auto adjusting.

Last height sensor I did I just put the suspension in off road and did it on the ground but obviously your won't go that high!

Technically you should re calibrate after changing but if you disconnect the battery you should be OK! 

batterys off already and it refuses to budge from the bump stops so no worries on that front pal

Update , new front left height sensor fitted , codes cleared , car immediately leveled out at the front but rear dropped toggle was lit but flick it euther way and it flashes with no movement , been for a drive , no change , pump looks brand new to me , got a new code
103 too much energy for regulation
Whats that mean exactly ??

Halfway there!

I'm not exactly sure but think it means one of two things:
1) The pump hasn't got enough power to regulate the pressure in the tank / tank is leaking

2) One of the springs is leaking and it can't keep it pumped up!

What fault reader are you using, does it show live values ? 

Ok , im using solus and i made a vid of the values , shall i email it to you pal ?

yeah can do mate,
Just had a look in the workshop manual, and the mention of energy leads me to believe a leak in the bag!

I take it the only way to check for a leak when its on the bump stops is to jack each wheel up in turn ?

Update , ive cleared faults and got the passenger side to go up and down but not
The drivers , compressors is running on demand , no codes for anything at now , help !!!

Update , ive cleared faults and got the passenger side to go up and down but not
The drivers , compressors is running on demand , no codes for anything at now , help !!!

Making progress , got the car at level ride height , so went for a drive , bong air susp inactive ! Code is 100 air validation fault , tried 3 times and the same one returns , whats it mean ??

Articulation validity?

Sounds like one of the airbags is leaking 

Ok but both rear height sensor control arma were in poor states , osr was seized on the axle and the nsr is broken at the bottom due to seizeing ( i think ) thow it still works ! So , if neither of those issues can cause that fault then i will try soaping each bag tommorow morning

Oh and another thing , the new left front height sensor is reading minus when the car is level ?? Wpuld this confuse the susp computer ?