Ok . this has probably been said on several threads ...
You have a 7.2 three stage motor as standard , UK suppliers seem to charge a fortune for these and they offer little or no performance advantage over the 5.7 which is often half he cost .
Your options are ...
replace the 7.2's and look for a good price on the net ( anything from 160 to 260 ! each )
fit 5.7 motors by slightly altering the mounting brackets . ( get the 1400/1500 three stage 230v )
Lamb ametek (mexico) are around 110 from accessoryplanet.co ..... or the cheaper e-bay 5.7 ( jackson spares )are from ameteks european plants . start at 55 .
option c .... fit two 6.6 motors whch are available from accessory planet for 140 , but you'd perhaps be better to get them from worldofclean for 160 as they hav the vac tube fitted , which u need .
these will give you 40% more air flow over the 5.7 .... lift is slightly less , but not significant .
I'v read they have the same mounting pattern as the 7.2 .... but that would have to be confirmed .
Might just add his edit to above ... you are using 1/1/2 hose , therefore you might not see the full benefit of increased airflow as using 2" hose with the 6.6 . You could convert the machine outlet barb to 2" and get 2" hose of course .
two of these Italian ameteks would be a good low cost fix , IMO
http://www.ebay.co.uk/itm/Ametek-Premium-3-Stage-Tangential-Discharge-Motor-5-7-240V-1500W-/180930091698?pt=UK_Vacuum_Cleaner_Bags_Parts&hash=item2a20461ab2