what are the chances of homebase replacing my paint without me taking it back?

[Sinistra]

today i bought some red paint from homebase, and had it mixed from one of their colour swatches. when i got the can open, it seemed to be much runnier than all the other paint i've used so far(and also had mixed there). i tried putting it on the walls, in the hope that it'd be OK, but it came out really patchy and spread really thin - of 2.5 litres, i'd used a quarter of a tin and it'd covered about 10 square metres!

in trying to take it home for my dad to look at, the tin has fallen over in my car (brand brand new 4 weeks ago!), and i now have a damaged car floor and practically no paint to return to them - what's left is swilling round in a plastic carrier bag, which the tin was in on the journey home.

all i'm after is for homebase to replace the paint (not cover the damage to my car - even though that would be nice), since i'm convinced there's something wrong with it. i've still got a receipt, just worried that i'll cause even more damage to my car if i try to take it back.