My first thought, upon seeing your question, was that the use of any such adapter would probably conflict with the IET wiring regulations and/or the relevant approved code of practice. The quote below seems to suggest that I was thinking along the right lines:
"[Q]: Can I get an adapter to charge multiple devices from a shaver socket? I want to charge a toothbrush and shaver from one socket.
[A]: Yes and no.
Generally speaking they do not exist from reputable sellers. I have seen some, but we have questions about their safety and reliability.
The sockets are not designed to take ‘extra’ strain.
You are best powering or charging each device independently as and when you need it. For example, connect and charge your toothbrush, when that is done, connect and charge your shaver or other appliance".
Source:
https://www.electricteeth.co.uk/2-pin-plugs-adapters-toothbrushes-explained/