Like Meadowman, I too am ex-Britannia ( retired about 6 years ago )
It is worth adding that the 50% discount on Thomson holidays applies only if the accompanying flight is 'charter'. If it is a holiday with a 'scheduled' flight, the discount reduces to 25%.
The maximum holiday cost of £1100 per person has been the same since the early 1990's and has not increased with inflation. This would indicate that the company are not too keen on this particular perk.