After numerous e-mails, got a phone call from the VWCS case manager.
It seems she cannot authorise a warranty repair as the supplying dealer, VW Telford has told her that all the GTis they supply have distorted bumpers! This is after I sent VW Telford, VW West London and VWCS enough pictures comparing my wonkey bumper in to 17 perfect ones.
She did not even bother to call the bodyshop for their input! I asked her if VW Telford had sent her pictures of all the distorted bumpers on their GTis. She said 'no' and could not discuss the matter any further.
She knew I would not be happy with this result, so she has referred the matter to the 'escalation team'.

VW and their dealers are quite disgraceful IMO.