If I were you, I would sync and edit at 24 (or 23.976 if we are splitting hairs) and convert the end result to PAL 25.
I work here in Hollywood in 23.976 progressive HD and, when finished, high-tail it to a small local post production facility for the final master output and the conversion to PAL HD 25 progressive.
As for the best system to use for the final conversion, I wonder if you use Teranex convertors in the UK. This is a real-time standards conversion hardware box of tricks which would normally be available at a mastering facility. If not Teranex, there clearly has to be something similar used in the UK.
If you are not massively knowledgeable or confident with Compressor, Cinema Tools and the like, I would stay away from attempting this conversion yourself because your broadcaster's Quality Control department will toss it back at you for the slightest infraction of standards. Here in Los Angeles, there are hits out on those QC guys.
I have found that it's well worth the relatively low cost of having my work converted by someone who does this all day and really knows their onions. There are all sorts of wacky things that can go wrong and which you personally may not notice, but which even a moderately priced facility will avoid.
Re: your last question: my movies get converted from 24p NTSC HD to 25p PAL HD all the time. One can set the Teranex (or similar) to convert your film so that you do not get a double frame once per second, which would look nasty, and so that the film retains the same running time. I know that sounds impossible. Just believe me.
Stop worrying. Cut the film at 24 and do all the audio at 24. Then totter round to your local friendly post production house and throw yourself at them.
well, standards conversion is one thing, but the majority of film to PAL (well, Pal is dead, 25fps) is done by speeding up to 25, and do some work on the sound to keep the pitch while changing the speed.
(some prefer different routines / settings for music and voice, but that's up to you.)
This does nothing to your video, and is free. (Cinematools can do the video, sound to your liking in any package)
I do agree to work in 24 / 23.976 (whatever it is now) and do the speed up at the very last stage. Another advantage this way is that you can crank out an NTSC version with normal pulldown if needed.
Do a bit of math before the edit so you know how long the final show will be. (that's easy math :-)