Thanks for your reply Onion.
I've just contacted Dyson who were very helpful and said I should return this one and they will send out a replacement.
Hopefully I'll have better luck with the replacement

Just thought I'd mention that the mini turbine head on my previous dyson worked really well and had excellent suction so I'm sure they are supposed to be better than the one I've got. It's as though there's an air leak or the sides are not sealed properly. Anyway, great customer service from Dyson.