Just a quick post to recommend this stuff from Screwfix. This Chain and Cassette were absolutely filthy with years of ground in oil and dirt. I initially tried scrubbing them with Muc Off drivetrain cleaner but gave up. With this stuff I just soaked them overnight and look how they've come up. Not bad for ten quid.
https://www.screwfix.com/p/no-nonsense-heavy-duty-degreaser-5ltr/88668



https://www.screwfix.com/p/no-nonsense-heavy-duty-degreaser-5ltr/88668