Having spent close to a whole day at TNA making copies of one year of the war diary of 2nd bt royal west surrey regiment and days thereafter trying to read my pics, I now find that I could have looked at them on the regimental site !
I hadn't looked before having read the official history with much disappointment in the lack of detail about "ORs"

So if the unit you are looking for has not been digitised, then it would be worthwhile looking at any regimental pages, official or otherwise, in case someone has done it independantly of the tna.

We live and learn.

Cheers Ed