Thought with today's supermarket petrol cuts that would include the momentum as well, nope price stayed the same £1.20 a ltr, is this the norm is it, how to they justify the hefty price tag for this stuff anyway. 

Tesco Momentum is normally pegged at 5p above normal unleaded isn't it?

Have to consider that supermarkets don't actually make much out of petrol at all so they find some margin in the higher octane stuff. Mankee is right that and v power are usually that much above whatever the bog standard unleaded is. It's justifiable as it's higher octane, more complicated to produce and they sell less of it. We pay tge extra but get the benefit of it being better for performance and mapped engines, more economical and just generally better. V power also has pretty powerful cleaning properties that you don't get in ten a penny unleaded, I think it's worth the extra.

For what it's worth I recently acquired a Saab aero 250bhp and the previous owner was putting any old unleaded in, got it on the v power now and after 1 tank full it already feels better and gives a bit more mpg. Not to to mention the fact that high octane fuels are actually recommended for higher output cars.

There was a thread a while ago about 'fuel in a vrs' which had some very informative stuff from people in the industry. Read that and you'll know why it always costs a bit more.