.popover--mainNav,body/.popover--menu, ","event":"layer-destroy"}],"events":["trigger"]}" data-t="nav">
Smarty (Owned by Three), Giffgaff (Owned by o2), Voxi (Owned by Vodafone), as well as the likes of Tesco Mobile (o2), Lebara (Vodafone), Vectone (EE), Lycamobile (o2), 1pMobile (EE), China Mobile (EE), Superdrug Mobile (Three), and Asda Mobile (Vodafone) to name a few all do SIM Only plans. Most are really competitively priced especially if you go via a comparison site. There's often no contract, and you don't need to worry about the price going up due to inflation.
If you do decide to go with one of the others, you would need to make sure your first bill was generated on or after April 1st for most of the networks. But it makes sense to check with the company beforehand to be sure.