Paying for Upgrade

What is the likelihood of being able to pay for an upgrade from Economy (X-class) at Heathrow - or, of giving a personal 'tip' to the check-in staff? Could they oblige?
quote:Originally posted by Flyer
What is the likelihood of being able to pay for an upgrade from Economy (X-class) at Heathrow - or, of giving a personal 'tip' to the check-in staff? Could they oblige?