Well all the original discussions were via email.
I've just wangled it so I am now working overtime on Sunday and I still have Monday off so I've phoned up to confirm the booking and spoke to a chap called Jason.
The remap will give me 290BHP...Not the 308BHP that they kept assuring me I would get. Apparently it is possible but its there 'race' map.
I'm happier going with the 290BHP option as this seems to be a proven and reliable figure for this car.
Its booked in and I'm going midday Monday.