I don't think they officially opened as they were completed after the air raids finished. However it is known that people did shelter in them, possibly unofficially and certainly before they were completed.
The tunnels would have had an official ticketing system but in reality during the war people wouldn't have been turned away unless they had become over-crowded which was unlikely.
In a time of universal deceit - telling the truth is a revolutionary act. George Orwell
When the debate is lost, slander becomes the tool of the loser. Socrates