the US never ever extradites US citizens to the UK for any reason whatsoever
Vociferous, I’ll refer you to this post from 2012, which points you to a written answer in Hansard from late 2011, which will provide you with the minimum number — a positive integer — of US nationals who have been extradited from the US to the UK. (Extraditions from the US to Scotland were not included in the answer.)