I've phoned Amberley museum today and they are happy to accept more Sinclair C5's for display at this microcar rally.
You will need to email office@amberleymuseum.co.uk and ask for an entry form. Once they have received your completed entry form they will then post you back an entry pass for the day,granting you free access to the event.
It's not long until the event, so anyone wanting to join in should apply asap.