I've just purchased a DC27 and noticed that the dust canister has a lot of free play when attached, plus the seal to the vacuum isn't very good - there is a big gap. I went back to the shop and every single Dyson of all models has this exact-same gap. Surely this is bad, how can it be an intentional design feature?

Hi Sunking

If I have understood your question correctly this is quite normal. The gap is intentional and you should find that when you turn the machine on the suction causes the rubber seal to stretch up against the sealing face. Having an oversized seal as you might expect would make the canister difficult to re-attach.

Why not just have the dust canister click-in flush against the seal? Other manufacturers manage it. I'm worried that when the machine is switched off and the suction gone, the seal will be open allowing allergens to escape from the dust container. Not good for allergy sufferers? Have Dysons always had this gap or is it a new 'feature'?

As far as I can remember they have always done it this way. The gap is quite small and the machines are accredited by the UK Allergy Foundation so you would hope that they have assessed it to ensure that any allergens esacape is minimal but it's a good point.

The pre-motor filter casing seal is also gaping open, why do these seals not fit flush for goodness sake?? There is no possible excuse for it.