If you're hoping to see Placido Domingo impersonating a baritone live from New York on Saturday, you've left it a bit late mate. Most of the London cinemas showing Simon Boccanegra sold out of tickets ages ago.
However, there is still hope. At the time of writing, the Picturehouse cinema in Stratford East still had a fair number of tickets left. And although the Barbican screening and BFI IMAX screenings are currently sold out, both permit customers to return tickets, so if you keep checking the websites you may get lucky. The others operate strict no-refund policies, but it may be worth turning up on the night and seeing if any customers have spare tickets to sell - this has worked for me in the past.
This is a list of all the London cinemas participating in the Met's Live in HD season:
And here's a full list of all UK cinemas.