Re Heathrow director's response.
Never worked at LHR, probably never will, but for a bit of possibly pertinent context, our MATS (which was based on the UK's years ago,) does have an allowance for permitting runway use clearances, without condition, if no conflict is possible. It may well have been this scenario. Obvious to some, but perhaps not to all that a such a clearance maybe shouldn't be issued if it is likely to cause concern, eg your situation, if night or IMC, etc.
Either way, definitely worth checking out, if only for your own peace of mind.