Speaking as somebody who (for reasons too implausible to repeat) is committed to doing a timeline of a Canadian version of "Babylon 5" starting in 1989, I may have some useful insights here. They are
- If you are doing a British Star Trek in the 60's then you have to go the Roddenberry-meets-Lew-Grade route. This is problematic (you might end up butterflying away "Stingray"). But Lew was the only person who could realistically produce a military sci-fi series (in colour!) professionally enough for international distribution - contemporary BBC series like "Doctor Who" had to trade on things other than the efficacy of their SFX.
- If you are doing a special-effects show in England in the 60's then you have to have Derek Meddings involved at some point
- If you are doing a sci-fi show in England in the 60's then you have to have Shane Rimmer in a bit-part
- Look at the shows of the time. Are there any you could butterfly away to free up their cast? If you butterfly away "The Champions" for example, you free up Stuart Damon, Alexandra Bastedo and William Gaunt, who could easily be cast as Kirk/McCoy/Rand. If you butterfly away "Public Eye" you free up Alfred Burke (who was born to play Spock). And so on.
- Where is it filmed? Pinewood? Shepperton? Pick one, work out what else was being filmed there at the same time, and use their supporting cast and technical crew.
- Who is paying for this? Who is your producer, where is he getting the money from? He's the ringmaster and showrunner and has to get everybody to work together. Since your obvious choice is Lew Grade, that solves a lot right there but there will be ripples: if you cast Patrick McGoohan then eventually he (Patrick) will leave because he's too alpha male to cede control entirely
- What technical limits are there? Is this on film? (Crude) videotape?
- Bear in mind some choices will leave: Ian Hendry is a good choice but IOTL he left the Avengers to do films. People have ambitions which may not include a three-year contract
- It will eat up your life. I spent a couple of hours working out how the coordinates of a pointer on a Steadicam mount could be fed into a late-80's computer (the trick is to realise you capture angle and length of a telescopic rod on a rotating..er, rotaty thing). Just wait until you realise your main actor wants to work in the States...
- Who are the writers? DC Fontana invented the Vulcan mythos ab initio. Take her away, your pointy-eared green-blooded folk will be entirely different...
Good luck
Damn you reality!!!!
All excellent points, the only one of which I figured was the one about McGoohan. So probably based only on him, no more than two seasons of the show are possible in the 60s.
Of course I won't let reality stop my fantasy of British Star Trek wank.