I have the BBR stage 1 as well
Can't recomend them enough, although there are cheaper options, all I can say is that I have been totally happy with the conversion. The performance is staggering, for me the only problem is getting the power down with no LSD or suspension mods.
If you do it, get a brake pad upgrade as well.
I live quite close to Brackley, and will be happy to give you a test drive.