Hi Sarah,
firstly as one who inhabits the world of the scanner owner I can sympathise with your annoyance, although I would add that I see no real need for a change in the current legislation and suggest that you read what follows carefully.
As has been said, the STRICT legal position in the UK is clear:
While it is allowed to purchase a scanner it is still illegal to use such a device for listening to transmissions destined for what is deemed restricted broadcast; this includes ATC transmissions.
It is also prohibited to re-broadcast such transmissions (on the internet for example) or propagate, via any medium, specific details of what you may have heard .
However; in actuality the use of scanners to monitor ATC transmissions for the purposes of general interest, hobby or self-education APPEARS to be tolerated for the most part as long as the specific details of the transmissions are not disseminated to the general public domain.
Note that even an off-duty pilot or ATCO is not, by the letter of the law, allowed to listen to such transmissions.
My current understanding is, and I look forward to being corrected if I am wrong, that generic discussion about RT appears to be OK but specific details are to be avoided as far as possible.
I hope that this clears up for you the rather nebulous legal position that surrounds this issue.
It would have been far better if an explanation had been forthcoming from the start rather than just receiving a terse "you have committed an offence...." from the initial responder to your post.
And to address the real point of the thread;
Maybe the airline bung them some cash to bring their flight in after the official closing time?
The amount involved is probably not as much as the one-off cost since it would be a guaranteed and regular revenue for the airfield but I'm guessing that shekels change hands somewhere along the line to allow that flight to land on a regular basis.
Cheers