If I am not mistaken, the £1 would typically be distributed between all of SVB UK's current shareholders. If SVB UK is 100% owned by the SVB parent company, and SVB parent is bankrupt, the £1 will get added to the funds that will make the SVB parent's creditors "whole", who outrank shareholders in bankruptcy.
Doesn't really matter. Whoever gets it will probably drop it and lose it at some point when he buys a soda or empties his pockets for the washing machine
And yes, the £1 has to get actually transferred, it is important for legal certainty e.g. with regard to https://en.wikipedia.org/wiki/Consideration_under_American_l....