For those of you who are used to popping down to the local police station to get a document signed by a Commissioner of Oaths, you are in for a shock. It is not that simple. Firstly you need need an attorney, a solicitor. Not just any solicitor, if it is for a document to be used elsewhere. For that you need a Notary Public.
I was referred to a web site https://www.thenotariessociety.org.uk/ for a list which gave me the option of just one. One who happened to be unavailable until next week.
So this is something, like most things, that needs to be planned well in advance.