Just as a follow up.
I found my event details and on page 3 it says
Withdrawals & substitutes
If you do have to withdraw before May, for whatever reason,
please inform us as early as possible. Substitutions will only
be permitted if there is no-one on the standby list waiting for a
place. Entry fees are non-refundable. Fees from those who have
to withdraw will be donated to a suitable charity or used for the
further development of the event.
You can find a pdf of the details on the TGO site HERE