I've been informed by Mike Meakin (Pembleton owner from Norfolk) about the Sandringham event.
https://www.sandringhammotoringpageant.co.uk/
Trikings are welcome to join the Pembleton pitch.
As a group we would qualify under their "Club" provisions (£10 a car including 2 admission tickets in return for display of cars from 1000 on the day). An alternative is "pole position" individual parking no admission tickets included). Public tickets £15 in advance, £20 on the day. Live music, vintage market, Spitfire flypast...Club displays.