I've just started this task - turns out a heat gun (or perhaps hairdryer) makes light work of removing it, tar remover/alcohol alone won't shift the cracked old trim. I also bought a plastic razor on amazon for £6 or so, works a treat for scraping it without damaging the paint - tar remover makes light work of the residue left behind.
It's possible to remove the old vinyl tucked under the window surround (vertical portion) just by opening the window and gently/temporarily levering the window surround to enable 4-5mm access, but the window bottom horizontal trim i've had to pop out to get behind and remove the old stuff, sadly this means a broken clip.
Anyone aware of the part number for the horizontal/bottom exterior window trim? I can probably push it back in again once vinyl re-fitted but if it's not perfect i'm going to replace it.