I think that if a non EU citizen flies into the EU (by airline) and then travels via GA, he needs a Visa, potentially in a lot of places.
First of all, immigration is not a EU thing but rather Schengen or national law for UK/Ireland.
Once you are in Schengen, you can travel as you like within Schengen. As to UK/Schengen, you will have to follow the typical rules for non Schengen arrival. Note that the Schengen visa waiver program (US terminology) is not restricted to airline transport.
There might be some exceptions. Indian nationals can travel to the UK without visa (correct?) but not to Schengen countries.
European Visa Policy