Random fact from the private discussion boards of Lib Dem voice:

Catholic priests were unable to stand for election to Parliament until 2001, when the law was suddenly changed, when, er Labour selected a Catholic priest.

Judging by the speech made in the Lords by Lord Bassam of Brighton, the prohibition was on both present and former priests.

Reading through the debate for a minute or two following on the link above, there are some fascinating contributions, including the 5th Earl Russell, whose book I haven’t read.