You can use advanced search to exclude items located outside the UK.
Many sellers in China have a distribution base in the UK, which allows them to list items as UK stock. All too often the item is sent from China anyway. If so, this is reportable to eBay using the reporting link provided in every listing (far right, opposite Postage and Payments).
Report Category: Select 'listing practices'.
Reason for Report: Select 'other listing practices policy violations'
Detailed Reason: select 'Item location misrepresentation'
Incidentally, if the item location is stated to be in the UK, you do NOT have to return it to China in the event of an eBay money back guarantee claim. EBay will require the seller to send a prepaid return label to their UK address. If it was stated to be located in China you would probably have to pay the return postage yourself.
Remember that if the seller is in China, there is a risk that the item will not comply with UK safety requirements, even if sold as UK stock. Regardless of where the item was located, you either won't have any statutory consumer rights or won't be able to enforce them.
