I have had a look at pc service call click here who look after PC World's aftersales support and they say that Lexmark service their own products:
Lexmark™ contact information
Lexmark International Ltd
Little Marlow Road
This machine is serviced by Lexmark™
Inkjet Support 0208 280 1701
Laser / Other Support 01628 480 640
Fax 01628 481 894
Not sure where you stand without having a reciept though.
Hope this helps in some way.