Dear Mary: How do I stop guests at my overseas properties leaving with the plug adapters?

Q. I have become a lodger in a fortunate friend’s flat in Mayfair. We are both single and I am keen to start giving parties there. I had a trial run which was successful, bar the presence of one inebriated guest who went around indiscriminately insulting people – for example he walked up to a female guest and swore at her, before jeering at another guest’s hairstyle, proclaiming: ‘Only a Nazi would have hair like that.’