Bananamanuk - got some more information for you from the Flightstats website. The aircraft came into GLO yesterday at 10.27 from DUB as RE4021. It departed GLO at 18.13 arriving in DUB at 18.48 as RE4022.
I think the conclusion on this one is that as previously mentioned it was a Horse Racing charter for punters having an afternoon at Cheltenham.
Let's hope their winnings more than covered the cost of the charter!