After checking the Xena site, I confirmed that the XN14 disc lock fitted onto TW200s, which have the EXACT same running gear as the TW125, only inside the actual engine is different.
When it arrived, it didn’t fit.
Xena said ‘a TW200 is not a TW125. Sorry, we can’t help you’
Luckily the dealer let me swap it for an Oxford Boss. I’m going to write a letter, this screw up cost me about £20, and Xena has lost a customer for life.