Presumably, the Senior Manager is either Martin Broughton, Willie Walsh or Keith Williams?
........... unless you're a BA employee, you're unlikely to know any of the others!
There is no way, however, that they would have avoided the UK Border Agency's Customs or Immigration checks. Apart from visiting Heads of State or those with Diplomatic immunity, everybody must go through the standard UK Border Agency checks.
If a senior, high-profile manager such as WW was to exit the building without passing a UK Border control point, British Airways' would immediately be forved to suspend operations at Heathrow - it would be traeted that seriously!