Not really, no. The Butex process ran at sellafield from 1951 to 1964, only the period of 1951 to 1958 was producing material for the UK nuclear weapons progra

Not really, no. The Butex process ran at sellafield from 1951 to 1964, only the period of 1951 to 1958 was producing material for the UK nuclear weapons program, after the successful hydrogen bomb tests the UK signed an agreement to a) use US nuclear warheads in UK bombs/missiles, and b) provide the US with plutonium from sellfield in return. The Purex process, which ran from 1964 til last year at the Magnox plant, and til 2018 at the THORP plant for AGR reprocessing, was the reprocessing process that replaced it, and only ever provided nuclear material to the US*, the UK never used it domestically. * I'm not 100% sure on this, since several EU nations used Sellafield/THORP to process their waste, I would imagine France at least wanted their plutonium for their own nuclear weapons back, but I don't know to what extent France used sellafield vs their own reprocessing facility in Marcoule