I wonder if this is Electrolux's answer to...
...the Sebo machines and the new Miele upright.
Rob: I would have thought the windtunnel ducting would enhance the pick up performance, as US Hoover said it picked up more than the Dysons did, and it prevented re-scattering of grit back into the carpet. See if there is anything obstructing the ducting; for example, paper, cellophane, etc.
Are you sure that the agitator belts are in a 'new' condition? (I read somewhere that US Hoover Windtunnels go through belts quite quickly; may be true of the Vax version, too).
Is the 'height-right' control properly set for the type of carpet? (I'm not being funny, as I've recently discovered one of Mum's Hoovers works better on a new area rug with a different setting than normal).