Thanks! Handy to know.
I spoke to BMW directly and they confirmed exactly what you just said above - £845 Comp, £709 Named and £551 Driveline, all with £250 excess and no roadside assistance. It's not as expensive as I was expecting in all honesty.
Did a bit more research and put together the following (might be useful for anyone else in the same position):
I'm fine with those running costs. Insurance, will be able to find cheaper if I speak to Adrian Flux/Chris Knott etc. Warranty, understandable uplift, but might be able to buy additional years from BMW at point of sale for reduced cost (asked for more detail on this). Minor service, same cost. Major, double the cost from BMW but can half that going to a reputable specialist (used Darren Wood before). Tyres, yes, expensive but I only do 5-7k a year so a new set will last 3 years minimum (will also try to push BMW into fitting a new set to the car if questionable tread left on current set). Discs, a set should last 20-30k miles, so no concerns there (ideally find a car at around 30k miles with them already done).
Pretty sure I've covered everything apart from fuel (worse MPG so will obviously cost more in general).