lets see
1) Offence only committed when crew report for duty and are over the defined alcohol limits. Therefore no offences reportable by the Police have been commited. CAA/Company regulations may not have been adhered too.
2) BA have no presence in MAN anymore. Therefore the 'Manager' who was dispatched would have been LHR based. Earliest flight LHR-MAN is 0635hrs, (if on-time). Manager would not be at hotel until at least 0900hrs. Cannot dismiss idea that Manager may live closer to MAN than LHR but would have to be contacted and briefed and then make own way.
Point is no BA Manager could confirm the allegation as it occurred or shortly after.
3) Flight deck could have, but having been woken from rest they would have issues regarding their own rules re rest and duty, whether allegation true or not.
4) This crew have two local nights acclimatization in JFK prior to flying to MAN. Therefore bodyclock could be JFK time of 2315hrs.
5) As always innocent until proved guilty. BASSA web forum has been locked on this issue. The last I checked the BA company crew web forum had no apparent mention of the issue. The allegations are being investigated and idol speculation is clearly not invited or indeed helpful.