Jaberwok
The Act of Union 1707 states quite clearly that for Scotland to regain independence both Westminster and Holyrood have to agree a referendum to decide the matter. Its like The Treaty of Utrecht regarding Gibraltar ,both sides have to agree in order to break the treaty. As it stands no way is Westminster budging on either of these issues
The Act of Union 1707 states no such thing. Maybe you are thinking of the Scotland Act `1998.
The Parliament of Scotland in 1707, like its counterpart in England, was made up of a landowning elite, many of whom had lost personal fortunes from investing in the Darien Scheme (note that the Scottish treasury itself was not bankrupted. The idea of consulting the common people about anything was beyond thinking about. As it happens, the Act was deeply unpopular among the Scottish people of the time and if such a referendum were to be held it would certainly have resulted in a thunderous NO! Union was opposed by both Catholic highlanders and Lowland Covenanters.
The union in fact was far from an amicable agreement anyway. It was an act of blackmail. A shotgun marriage if you like. The English parliament was terrified that after the death of Queen Anne the two crowns would be separated again, with England committed to a Hanoverian succession and the Scots free to appoint their own successor, presumably James Francis Edward Stuart, the Old Pretender, as James VIII, whom many Scots saw as the legitimate king anyway. The English were further concerned that Scotland, a long-time ally of the French, would interfere with England's wars with France. England had been blockading exports to Scotland for two years and had decreed Scots in England to be foreign nationals. The members of the Scottish parliament were bribed with reimbursement of at least part of their Darien losses, but if in spite of all that they did not cooperate then there were troops stationed at the border ready to invade.
But under the terms of the act, it was always a "voluntary" union. Even Margaret Thatcher said, 290 years after the act, that if Scotland wanted independence then all it had to do was elect a pro-independence majority to Westminster. That was fulfilled in 2015.