No, sorry, what ex EU means is you fly to a country outside of the Euro zone, say Sweden for example, so one that doesn’t use the £ or the € as its currency, and ‘start’ your trip from there. You book and pay for your flights in the local currency (after doing a currency conversion to check the price against the £).
The timing can be crucial though if you don’t intend to stay overnight at your ex EU destination as you’d need to build in enough time for a flight to land, collect your bags, re check in etc.
Reading this back, makes it sound more complicated than it is in practice.
What I’m trying to explain (badly) what we’ve done in the past is this:
fly LGW to Oslo mid afternoon on a Monday
stay in a cheap airport hotel overnight
fly to Sydney from Oslo on Tuesday
Then route home the same as the outbound, minus the hotel overnight in Oslo if you land early morning and get an afternoon flight BACK to the UK
Paid for the LGW to Oslo return in £ (flown BA for example)
Paid for the Helsinki to Sydney return flight in Norwegian krone
The general rule of doing this is the amount of money you can save on APD as it’s much less from outside the UK. However, if you’re time restricted then it’s not always ideal as you’re adding additional travel time. We usually fly business to Australia so this way of going about things has saved us hundreds of £, I’m not sure how much you could potentially save if flying economy or premium economy.
Happy for you to PM me if it’s still unclear.