Not sure if the Quidco will work for all, but the money has tracked for me already (after you have completed your stay).
Go through Quidco, search for Intercontinental Group Hotels and click on their link.
When the Holiday Inn Home Page pops open, manually change the address to http://www.ihg.com/somerfield.
and search for your required booking.
On the front page of their site it does say this is for 'weekend stays', but I've done a couple of searches and it definately gives a discount for midweek too.
The discounts seem to be 25% of midweek stays and 35% off weekend stays. The offer claims it's available at over 200 of the Crown Plaza, Holiday Inn and Express Hotels.
It looks like this runs right up to 31st December 2009.