I'm 25 miles from LHR and looking out of the window at the perfect visibility. Whatever the arguements about long term engine damage, there is no way that an aircraft would be in any danger approaching LHR today.
If the CAA (or NATS) force the BA inbound aircraft to divert to another airport within the Met Office 'guess-map', then somebody needs to question their judgement.
I think you will find that they already have been forced, MAD, BCN and NCE.