Surely as of 1603 the crown of Scotland (James 1/6) was sovereign in Scotland and when the Carolinian line became subject to the will of parliament (or, if you prefer, the will of parliament was re-asserted, since the "divine right of kings" was a continental concept) that was as true of Scottish law as of English.

Both Scotland and the Isle of Sheppey are parts of Great Britain.

Any part of the UK could secede if so permitted, and it may be that the present politically correct regime(s) would so permit, but the law should that permission be refused seems to me to be that only by right of eminent domain (translation: = effective revolution and subsequent long term stability) would the constitution be amended.