So I ended up here in 2013, and I had no answer.
After going there: http://support.vax.co.uk/faq/faq/view/id/356/
I checked the hose, and sure enough, there was a lot of crap jammed in the plastic handle. I cleaned it out using a coat hanger wire that I turned into some sort of hook, and went fishing for dust fluff. Turns out that there was a bit of CERAMIC TILE stuck in there, and that all the crap just piled on it.
I also cleaned the bag's air filter using a fork (to get as much of the big bits out as fast as possible) and once most of the stuff was out, rinsing it under the tap, spreading between each crevice to get the flow to flush out the remaining dust.
After that I jammed everything back together, put it on full blast, and the vacuum cleaner regained suction progressively, as the filter dried with the air flow. You could also not be stupid like me and let the filter dry by itself.
#YOLO
Frank
October 2013
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vacuum cleaners.