I tried supermarket own brand toilet gel - and the winner is just as good as Harpic or Duck and a third of the price | The Sun
Toilet Cleaning Gel for the Bathroom | Clorox®
Amazon.com: Lysol Click Gel Automatic Toilet Bowl Cleaner, Gel Toilet Bowl Cleaner, For Cleaning and Refreshing, Mango & Hibiscus, 6 Count (Pack of 1) : Health & Household
Amazon.com: Simple Life Toilet Bowl Cleaner | Fresh Flower Gel Stamp | Stops Limescale and Stains with Air Freshening Scent | Deodorizing Clean | 32 Stamps, Blue & Green : Health & Household