Hey, I don't think this will work for the Masuda Method. If I'm accurate, I believe you need (indeed) one of the parents to be caught in your own game cartridge, and the other has to be from another country. Since you live in Europe (or have at least a UK cartridge) you will need another parent to be from i.e. a Japanese cartridge (with the JAP tag in the stats) I believe, because France doesn't count as "the other foreign parent" here, because France is (like UK) also in Europe. So you will need a JAP Pinsir or a JAP Ditto :) Just to be sure ;)
I'm currently breeding for a shiny Fennekin using the Masuda Method, and I have one Fennekin parent of my own cartridge, and the other Fennekin parent is JAP. I'm living in Europe, so I couldn't use a French/German parent etc. either. Hope I helped and good luck! ^_^
Neither parent needs to be caught by YOU.
You simply need two Pokemon from differing regions. One parent can be native to your region (it will not display a tag if it is native) but this is not required. You can breed a FRE and JPN, a KOR and GER, an ITA with a SPA, ect ect ect even if you have an English/UK game. However in your English/UK game if you try to breed JPN with JPN or GER with GER, MM will not work because both parents are from the same region (even though they are "foreign" to your game they share the same region tag and therefor MM will not work). MM only dictates that the parents be from differing regions. It doesn't say one parent needs to be something you caught personally, or that one parent MUST be from your region.
Proof: I got an Altaria from WT (native to my region but not caught in my game), bred it with a JAP ditto, and got a shiny Swablu in just under 50 eggs. I hatched my banana yellow Swablu today on my lunch break and was super excited!
My next MM attempt I am going to try to use two foreign Pokemon to prove that I can obtain a shiny without using a parent Pokemon native to my region, because everywhere I read it says "breed one from your game with one from a trade", but I think this is just because it's the easiest way to set up MM breeding. I am convinced two foreign parents can be MM bred as long as they are from different places!
Regarding you being in UK and unable to use FRE/GER Pokemon for MM breeding: do you have any FRE/GER Pokemon you got from trades? If you can see the region tag they should qualify as a parent for MM breeding with one of your own Pokemon.
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The rest of you considering MM breeding: do it! It may take a while, but finally hatching your shiny baby is worth the struggle of hatching 30, 50, 300 eggs. Plus in the end you have tons of (hopefully) decent babies to throw into the WT and maybe you'll get something neat in return!