The UK doesn't have the supply chains to support the rest of Europe. There are lots of parts on an F-35 that the UK can't make; despite being a Level 1 partner I don't think they have the full technical data package for everything. But neither does the US have the supply chains to support ourselves without the UK, especially for the F-35B model. That's why this whole dispute is so stupid, and hopefully cooler heads will prevail.

https://ukdefencejournal.org.uk/how-much-of-the-f-35-is-brit...