Answers on the bottom row are entered backwards; answers from the bottom half of the last column are entered backwards .... hope this helps. The unclued entry could be "trail ones coat tails" but I could be wrong. 22d is MICROHM (entered backwards) and 5a is CESTOIDS (right way round). Suspect similar rules for clues starting in the first column - i.e. half to be entered backwards.
I also have S?OM. Don't know what's going on! When I first replied to this thread I only had half the grid completed so I'm waiting for someone (usual suspect) to ridicule my suggestion for the unclued entry ....
thanks
things are a bit hectic with me at the moment as I await news of my Gran (very ill) in between hospital visits 70 miles away (I'm her only relative!). Will probably not get finished this week as a result, but will try to keep up with the thread. Sorry for not being much good at contributing. Will probably have a lot of questions when things die down, so hope you'll all oblige as usual