when can I go round for a cup of tea?
It's complicated. My Dad got the Pfzier vaccine yesterday (mid 70s but extremely clinically vulnerable). Different to the Oxford vaccine, but it will take 12 days to even start doing anything, a few weeks after that it should typically be 52% effective.
He's due to have his second dose on the 2nd April, a week after that it would typically be 95% effective.
All this aside, the vaccinated will have to follow the same rules as everyone else because the advice after you've had the first jab is to act like you've not had it, then even when you've had the second you may still spread it.
So although my Dad will be as safe as he's going to be from 9th April we've got to hope that infection rates will have dropped by then and social distancing rules relaxed.