Okay half the problem fixed .
The standard Aux drive belt is a 6PK1420. If you bypass the Aircon Compressor and the idler pulley above it, a 6PK1290 belt works but there is only 6mm clearance between the run of the belts, and at tickover they just kiss together. Using a 6PK1275 belt gives 22mm clearance between the runs, and other than being tight to squeeze on works fine. So instead of having to buy another compressor just to be 'in circuit' for £40 I have a working solution, which if I had been more luckier/accurate would have only been £20.
If I had to do it again or if someone else has the problem, then I would suggest using a 6PK1280 belt which will give adequate clearance. and be a shade easier to fit.
The hardest part of the job is taking off (& putting on) the 'elasticated' power steering belt which when working in the drive, in January, wasn't the easiest of tasks, but competed satisfactorily all the same .
Now to look at why the lights pack up...............