Another G4S special lol...
All you require is a gap reference for the dates required from a responsible job holder: teacher, Civil servant, Police Officer etc saying that between these dates you were....
Ask G4s how you would get a reference from a company that has gone to the wall?
I used to coordinate all ramp recruitment for a handling agent at MAN and gap references are legitimate means of reference but it is not very well publicised.
the DoT recognise this type of reference so why shouldnt G4s. Also when I have contacted HMRC for references they can give the dates you paid tax to/from on each employer, and as long as the gap is not more than 3 weeks (better check that it might of changed) you dont need a reference...