For what it's worth, the Notice states that tickets are available from TicketMaster, SELECTED branches of Barclays Bank (No clues as to which branches) and Robert Dyas.
The Store Locator for Robert Dyas shows they hav branches as below:-
NameStreetTownPostcodeTelephoneDistance1
More details for SWINDON 34 Regent StreetSwindonSN1 1JL017-9349-503610.19 miles2
More details for WITNEY 21-27 Market SquareWitneyOX28 6AD019-9377-813813.51 miles3
More details for CHELTENHAM Unit 2 206 High StreetCheltenhamGL50 3HF012-4257-025418.65 miles4
More details for OXFORD St. Michael's Hall Shoe LaneOxfordOX1 2DP018-6524-324322.31 miles5
More details for CHIPPENHAM 30 Borough Parade Shopping CentreChippenhamSN15 3WL012-4944-637622.63 miles
Now, there is no guarantee that these branches will have tickets, but perhaps there is a chance that people turning up on the day might be able to get to these stores (hopefully en route) or after arrival they may not need to drive all the way home....
Just a thought, it might save some kids day being ruined....