Probably a Thomson 752. The family of 3 got a spare seat for the daughter and galley jumpseats for takeoff and landing for the parents.
The crew may even have been within the regulations when they allowed the family to stay on board. The aircraft was not over capacity, and everybody had a safe seat.
Question is if the crew insisted on the parents getting out of their jumpseats when they started the service preparations, or just kindly asked them to consider it as a courtesy.
Even if no law or regulation was broken, this is certainly not what you'd expect when you book a flight, and 30 quid as a compensation offer is ridiculous. Still, I guess this was an isolated incident.
Let's just hope it won't give Ryanair any funny ideas...
None are more hopelessly enslaved than those who falsely believe they are free.
(Johann Wolfgang von Goethe)