Yeah I'd say go for the Complete set LE, I originally had only the 1973-74 sets when they first came out around 2004 but got the Complete one in 2013. The Complete one if it's still the same one has all the 1973-74 extras too.
Another thing with "Special Branch" too - I loved the Euston Films era titles and theme tune.
F*****g great stuff!
Though it seemed a bit of an anti-climax for the next 48minutes of story.
The titles, fast, pacy, shoot outs, a car crashing, people running down stairs, punch ups with bold music - and then more than often the story lines (though good) were never as pacy and quick as this!!
Not sure if the music was specifically composed for the series - though throughout the series you can hear stings and variations on the actual piece.
Not aware if it was a library peice, and Euston Films used all the various edits of it too.
Robert Earley wrote it all didn't he?
Frightened by Horror Films? - Just remember, BEHIND the camera stand even more horrifying individuals moaning about the Catering food, the hours they work and quoting Union Rules... that's just the Electricians.