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Hi Miles, thanks for your question. I'm happy to help and advise. Providing your printer is a UK bought printer, the cartridges on this page are the correct ones, The number in the product code you gave 436 matches CB436A so I believe they are the same but the code you have might be because its a manufacturer code of the brand you bought (assuming its not original HP).
With regards to whether you buy original or compatible, being absolutely transparent with you, the compatibles are great quality and are guaranteed for 3 years, however, the quality will never be completely equal to the original HP so if quality of print is extremely important to you, I'd stick with original HP. If it isn't, having something that is a great substitute while saving a lot of money makes sense! Remember that our compatible guarantee covers complete satisfaction so if you aren't happy with the quality, let us know and we can arrange a collection / refund.
If you need any more help, let me know.