Turkey Dinner was the Christmas episode that was shown on the 23 December 1974, it was from Season 7 and was episode 6. In spite of it being shown at Xmas time and involving Turkey, plenty of them actually, it isn't actually a Xmas episode. A lot of British situation comedies of the 70s and 80s would do this, have an episode shown over Xmas but not actually involve much, if any, actual seasonal flavours.
Dad's Army was a grandly written show that was performed with great skill and wit by the cast. This was a rare case where not a lot really happens and thus it just gets by on character affinities only. Plot basically has LCpl. Jack Jones (Clive Dunn) accidentally kill a Turkey and the group of Home Guard volunteers who he belongs to, first try to remedy the situation, and then set about making a big dinner for the pensioners of Walmington-on-Sea.
The customary vocal sparring pops in from time to time, while the rag-bag nature of the different members of the group is still mined for good viewing. Yet it's more safe than anything broad and essential. It's very much an episode for hardcore fans and not one for interested observers to sample as a starting point. 6/10