Another kick in the goolies today :-( Hagon have gone over my wheel with a magnifying glass and having looked at some stress points I've highlighted, think the rim too thin for the re-alignment. Basically, by having the spokes pull the rim off centre as it were, the angle out of the rim is causing things to distort. This is a poor rim that lacks raised 'dimples' where the spoke nipple exits the rim.
My only answer has been to buy a better quality new rim and get it drilled to suit. In fairness to Hagon, and by way of an apology, they are only charging for the rim and not the work (or re-work) so I thought I might as well get them to re-coat the hub while they were at it (and managed to blag a discount for that too :-))
Needless to say the credit card is taking a big hit for this one, so expect sulks and tales of woe, especially when Mrs C finds out.