That is not an option here on ebay.com, the primarily US site. You need to go to the UK site ebay.co.uk where the "Item location" filters available in the left column of search results (or on Advanced Search if you want to start there instead which I don't recommend unless you want to use one of the few options not available from the left column filters)*.
Keep an eye on your browser's address bar to be sure you stay in the UK site, especially if you are actually buying (or very especially setting up a listing to sell something) as there are links over there that bring you over here and it's easy to not notice the change until you have done something costly.
*ETA: are more suited to that geographical location, with "UK only" "European Union" and "Continental Europe" as options. And even the "Default" setting will be more weighted to UK items than over here (where many international items are not included in searches, and sellers often have to pay an extra fee to get them included in searches over here).
