First off thanks to Diana for pointing out there were some cuts apart from 
the credits and titles in series 1 and 2. I'll have to compare them to the 
UK TV broadcasts to see where these are – I've not noticed them yet!  🙂
Now to series 3 and 4. Basically they are 4 discs per series, 3 being 13 
episodes 30 to, 42, and series 4 is 10 episodes 43 to 52. Again these are 
Memphis Belle releases and I obtained them off eBay.
Unlike the series 1 and 2 discs I have which appear to be region free, DVD 
Decrypter reports them as region 2 DVDs (so anyone outside  UK, Ireland, 
France, Greece, Turkey, Egypt, Arabia, Japan and South Africa will have to 
check their player to see if it can play them)
As far as I can tell there are no cuts in the episodes (although I'm sure 
someone will tell me if this is not so). The first thing I noticed is that 
the video quality is noticeably better than the releases of series 1 and 2 I 
have, I would say as good as the thirty five year old tapes will allow 
without major re-mastering work.
Overall I'm pleased with the Memphis Belle releases – not perfect but 
acceptable for my needs (and considering I've managed to get all four series 
from eBay for about the same price of £39.99 for the new release of just 
series 1).
Hope this will be of interest to anyone considering purchasing these DVDs.
Bill.