You need to differentiate between receiving a pension at an allowable age either as income or a lump sum and cashing in a pension fund before it's due, reverting it to cash. The links given so far refer to the former. I believe the Swiss will tax you on the latter, at a rate that is equivalent to the rate if that was your only income in the year but maybe not if you're no longer Swiss tax resident? Not sure about the UK. If you're UK tax resident when you cash it in then probably it's UK taxable.



Talk to HMRC - the horse's mouth so to speak.
Or you just don't mention it.