Scottish Pound VS English Pound?

Dear Readers,

I am currently at London enjoying another Architectural Trip! :)
It is me here just came back from ASDA Troughton, Greenwich. One thing puzzled me, why they do not easily accept Scottish Pound here?

Any idea related to the UK Legislation or what?

I have been staying at Scotland but they accept English Pounds at large. Why not the other way round?
Is this another 'virtual image' created so to show Scottish Pounds somehow is not easily accepted at large throughout the UK~

I am eager to know. Please leave me comments.


Currently at London,
Zhen Ron.