NLH, thanks for that link and confirmation that there were actually 46 MPA Nimrods built. Th eoriginal order was 38 and a follow on order, the XZs were I think ordered by Ted Heath for the Malta Sqn (?).
PS, to add to that, the first XZ airframes began life, and saw service, as MR1s before being pulled for the AEW programme. Only the last XZs became straight AEW and even then they might have had MR tails first.
BAe accounting and contract meant they got a stage payment for the airframe when they were delivered to the RAF. Their accounting year ended 31 Dec. One year we had several undercoated jets lob into ISK about Christmas, only to be flown out the following days to be re-fitted. Wierd.