The bmi guys are leaving 'cos the LHR operation is about to be 'downsized'. Those at the lower end of the seniority list could be 'surplus to requirements' and either made redundant, or re-fleeted & offered positions in the regions. Cash is not the deciding factor here, morale is all-time low.
What with rumours of an ALLIANCE (read LUFTHANSA) buyout looming, and the Final Salary Pension Scheme in jeopardy, you can understand the desire to get out before the current supply of reasonable alternatives dries up.