and if you roll your car.. the £60 one or the £300 one is still gonna stop your head from getting fucked up. dont see a problem with a cheap helmet, as long as it isnt made of papermache then it should be ok.
Like others have said, surely it needs to have passed some kind of test to be allowed on the market, and if it has, whats wrong with a £60 helmet when its doing the same job as a £300 one.