This sometimes happens when you view or buy an item from an American seller, then everything is shown in US $$'s.
You need to log out completely, even shut your device down. Start up, clear cache and cookies, and log into your homesite, https://www.ebay.co.uk and everything will be back in Sterling Pounds.
If it doesn't switch back, just refresh your page a few times, that will kick start it into showing the correct currency.
@shaah1182
