I'm with Argos and had a large increase this year.
Meg's, who's 8 went up by £10 a month (sorry I pay by DD so can't remember the details) to nearly £30 but Jakey's only increased by about £2 per month to about £12 per month.
I did look into changing but pre-existing conditions are not covered if you move and Meg had a series of Anal Gland problems and I'm in the process of claiming for Jakey's bladder crystals so I guess his will go up next year.