the new Cadbury promo gives 50% off site prices, BTW (£16pp on off-peak days)
you're able to see the adjusted prices here: https://www.altontowers.com/?promocode=CADMULTIPACK26 - off-peak days are 50% off, so £16pp. however, peak days only give a 10% discount.
Currently, you can book up to Nov 8 (though the promo runs til 30 Jun 2027). one code allows you to book for up to 4 individuals (any children under 90cm go free - I assume you'd book this separately), each individual paying the adjusted price each.
This promo is available on freddo 4pcs, caramel freddo 4pcs, dairy milk buttons 4pcs, cadbury fudge 4pcs, curly wurly 4pcs, the 96.5g bags of mini fingers and mini animals, the 115g bags of snowy fingers, and the 78g/125g Cadbury selection boxes. You'll see the promo on the packet advertising "10-50% off" attractions (if it doesn't, it's not a valid pack).
You don't really have to buy them yourself as they only need the barcode and batch code (both of which are probably multi-use) which is on the back of the packs, however it goes through verification (it took a few hours for them to send my email with the code) so it probably isn't worth publically sharing any codes. I bought a pack of Freddos for £1. They tell you to retain the receipt for the product, too. The link to enter your barcode and batch code is here: https://fun.cadbury.co.uk/ and then you will get a code via email to input into the Alton Towers website.
I found promo packs in my local big morrisons, they should be easy to find in big supermarkets.
Hope this helps anybody looking for discounts! The Kelloggs discount is worse value for off-peak days, and also expires on June 30. If you're booking on a peak day (i.e., in the school holidays), it might be worth looking for a 2025 Kelloggs promo code which gives a blanket 25% off, converting your Tesco Clubcard vouchers into Alton Towers vouchers, or using https://www.daysoutguide.co.uk/alton-towers-resort to get 33% off (you need to buy a rail ticket to Uttoxeter/Stoke station for this to be a valid promo - see https://www.daysoutguide.co.uk/things-to-do/merlin-full-terms-and-conditions-2026). Note the daysoutguide promo expires May 31.