Thank you for the date on the front hub I do not suppose you know when the patent was approved on the AB hub which is on the back but instead of a date on the hub it is stamped into the metal patent applied for. I am still bearing in mind that as someone previously suggested that the wheels could have been changed as the difference in the braking system does not tie the bike down to a model.
Believe it or not I was on holiday in Wales earlier on in the year and spent some time looking at the national collection but I spent most of the time looking at road bikes and not the sunbeams they have there. Perhaps I will try emailing them to see if they can help with identification of the bike. Cheers