Thanks to MG John's post on this topic, and the advice from others that the plastic collar has to move fully forwards, I successfully employed the slim 17mm spanner method to separate the joint. These cars may at times be frustrating, but there's always someone who has been there before you and found a solution. This is the advantage of a proper forum, real enthusiasts, real knowledge, not the argumentative and fake stuff you tend to get so much of on Fakebook!
