With VS, there is a 'Mates' scheme for employee's (could be crew, ground staff, management etc) so that friends of the employee can have discounted tickets bought for them. There is/was a 'Mates Plus' where friends travelling with the employee can get upgraded when travelling with the employee. The benefit was scaled according to the employee's grade. Not sure if BA has an equivalent, but this would be upgrades/benefits in an official way.

Unofficial upgrades would be tantamount to a supermarket employee with staff discount buying goods to sell on to a person not entitled to the discount, for example.