The London government's new slogan, "Scotland in Britain", which is intended to get people to oppose independence, is ludicrous.
The name "Britain" is a translation of "Britannia", which referred to the whole island many centuries before it was divided politically into the constituent parts of England, Scotland and Wales.
When Ireland was politically partitioned, Ulster continued to be geographically part of it, and when Norway became independent it remained in Scandinavia. Scotland was part of Britain before the Union and would be still be so after independence.