You can get Black Rat by the pint in The White Bear and The Highbury Vaults on St. Michael's Hill.
The most lethal I've come upon is Exhibition served by the half pint in The Coronation Tap in Clifton.
( LimeyTreat Bitch. Lover. Child. Mother. Sinner. Saint., Sun 10 May 2009, 12:25, archived)

That's legendary
but we try to keep it secret.
( wynoh kills threads by his mere presence, Sun 10 May 2009, 12:44, archived)