Thanks to a very positive response to this, I have gone ahead and changed my reservation to a commitment.
So now I can confirm what a couple of people guessed: the venue is the Bicester Heritage site. We will have the entire "technical site" (ie not the airfield) to ourselves. This is going to be THE Abarth event of the year.
Tickets will be on sale early in 2018, but please etch the date in your diaries now.
And if you want to see what the location is like, don't forget that we are attending the Sunday Scramble there on Sun 7th January. See the separate thread for details on how to book tickets for that one.