None of the cases are known to have been hospitalised or died, but the UKHSA said that “most of the cases have a specimen date that is very recent and that there is a lag between onset of infection and hospitalisation and death.”
It follows concerns that Omicron is more transmissible than the Delta variant and will form the majority of infections across Europe by the New Year.
The UKHSA says 12 of the 22 known cases up to 30 November had been fully vaccinated.
Another two people infected had been given their first dose at least four weeks earlier.
Six were unvaccinated, with no data available on two of the cases.
The news broke as the first Welsh case of the Omicron coronavirus variant was confirmed on Friday.
The case is in the Cardiff and Vale University Health Board area and is linked to international travel, the Welsh Government said.
But Public Health Wales said there is no evidence of wider community transmission.
In Scotland, six Omicron cases were linked to a Steps reunion show in Glasgow.