You can find their advice at this web page:
https://www.u3a.org.uk/advice/running-your-u3a-covid-and-beyond/england-activities-advice which offers their advice. It was posted in mid-December 2021.
This address was checked on January 2nd 2022 but advice might change without notice. As far as is possible we will keep up to date with their advice but as things are moving so fast at times there will, inevitably, be a time lag both as National Office process changes and as we work out how to apply them locally.