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There's a bit of info about some of the common options in the broad spectrum (pun intended) of refinishing processes available for bikes - https://colecoatingsworkshop.com/process
Also, although not comprehensive... this person goes into a little more technical information but in the most part is referring to auto application rather than bikes, where there are many big differences - Jalopy Journal
I am sure Argos would do a wonderful job on it but I am not sure it would be £112 better. Plus that is their lowest price for plain enamel: metallic etc are all extra.