Thanks for the replies folks.
It would actually be four blokes in a C172 and so I think Upfield Farm would not be an option. At best I'd take 1/2 fuel load in order to remain within W&B so I'd need to refuel at the other end. The trip would be from Gamston.
The footy match is at Ninian Park (right next to a train station) so a train from Cardiff Airport and parking at the Academy on the south side seems the logical solution. But if there is some doubt as to whether we'd get back to the a/c to be away by 6.30pm, then the whole trip is in doubt as I have to get back in daylight (no night rating). Sunset is around 8pm at the end of April I believe (will have to check exact time) but unless we're airborne by 6.45pm I'd be pushing my luck to make it back to Gamston.
By the way, BFR passed, if a little rusty...
Regards.