I always limited my thinking on that 23D Trailer Caravan until today Antonin. You and I thought together on it, early wheels, and then later wheels. It seemed as though all the early versions HAD to have the early 8X18 knobby wheels on them until I really checked our collection over when thinking about large and small fine BPW wheels on the 45A. I actually noticed today that those 8X40 wheels were available for use on the early yellow Trailers with all the first casting details on them, possibly even as they were released to the public in 1965. We know the most common were the 8X18 BPW on all the early yellow variations, yet they are also all found with the 8X40 BPW to prove those wheels' introduction very early in this Caravan's production. I can't prove that Lesney did not have these fine 8X40 wheels in early 1965 because they were already using fine tread 10X36 wheels on the #28 Jaguar in May of 1964 a year earlier. These 8X40 fine BPW MAY have been available and used on a very last run of the 45As to end their production in 1965.
BUT, It also seems that if there really were two different size fine BPW on the last run of 45As, they also could have been the 'stock' 9X36 BPW as 'small', and then the 10X36 BPW (large) as both sizes were also used on the 38B Vauxhall Victor Wagon with red interior. We had found our 38B Wagon with larger rare 10X36 wheels in one of our U.S. stores in the 1960s, but Nick just documented it as a 'new variation' in January of 2010. Perhaps if we all look at these BPW 45As in 2015, we may be able to add the second size fine BPW variation Harold had noted in 1976. Harold is gone, but the models in his collection are still with us somewhere in the world for us to re-discover.
To a Very Happy and Productive New Year in collecting for all of us........

kwakers