Well the bird reappeared just after I made the original post and I'm able to add a little more to the ring code. I now know that the ring is LK3724.....?
Just got in from a late shift and downloaded another bunch of images that I'd taken just before leaving for work. Looking through this new bunch of pics has finally allowed me to put together the complete ring code of this bird. The final combination has been revealed as LK37249. Although I've already contacted Sandwich Bay Obs, I'll send this info to the BTO and see what I can find out about the journey this bird has made to reach my feeding station.