I got to thinking about this after answering a similar post on a Norton forum...
Due to considerations for the future, in my old age when I get to a point where I can no longer kickstart a bike, the last 2 Britbikes to go from my entire collection will be:
-My custom monoshock Norton with Spyke starter
...and my '83 Bonneville 8-valve TSS
However, if we get to make it a "wish list" of ALL vintage britbikes, I'd probably want an early girder-forked Speed Twin and a Vincent roadster.