A little post of mine on Saturday about Mary Lady Broughton widow and "Keeper of the Gatehouse Prison" (in Westminster), caught the attention of Sharon at Early Modern Notes. She shared her existing knowledge and added more, and has discovered a whole dynasty.
To continue the collaborative effort, a bit more on the gatehouse. It must have been a pretty grim place by the 17th-century, old jails usually being so. It was finished in 1370 "as the new gatehouse to the conventual buildings of Westminster Abbey at Broad Sanctuary. It contained then, or later, two jails: one used by the bishop of London for prisoners to be judged by clerical law, and the other for lay offenders. Both were administered by the abbot of Westminster .... The approximate site of the prison is that of today's war memorial to former scholars of Westminster School, outside the abbey". (From The Annals of London: A Year-by-Year Record of a Thousand Years of History, J. Richardson, Cassel & Co, 2000, p. 50) The Gatehouse was demolished in 1774.
The only reason most people would have to have heard of it is Richard Lovelace, the Cavalier poet, who was held there in 1642, when he wrote: “Stone walls do not a prison make, nor iron bars a cage; Mindes innocent and quiet take That for a Hermitage.” You can find out more about him here and a copy of the poem, To Althea, From Prison.