We also take ours to Griffiths for slaughter, the carcases then gets delivered to another butcher for butchery. If they are a little distance from you, then you could find out if they delivery regularly to any of your local butchers as that at least reduces your traveling for collection depending how far you are from Leinwardine. They also do pigs too.
Can sometimes have to wait a bit to get them booked in, however we rang last Friday to book 2 lambs and they went in Monday, but sometimes have to wait 3 weeks.
Re not taking them in December we had problems last year, however if you book well enough in advance then you should probably be ok.