Based on this site, the A55 should be supported by all UK networks, regardless of the whether it's the Global or International variant: https://www.kimovil.com/en/where-to-buy-samsung-galaxy-a55-5g-sm-a556e. I suspect the same will apply to the A16 (and any other current Samsung phones).
Keep in mind that there is likely some restriction on when the phone can be unlocked in order to bring it to another carrier. You may need to wait at least 6 months -- check with Tesco about this.