You can't trust those Oxford Schloars Q ;-)

The BBC link I gave, actually in the Douglas Adams HHGTTG area of the BBC site, and your link certainly both suggest the prison existed earlier than the Barclay 1515 Quote given above. Certainly the Barclay Quote seems to refer to 2 prisons, Fleet and Clink, in existence at that time. I don't have an OED handy.

That's probably enough thread drift here. This is supposed to be about the Australian online magazine so I'd better have a look at that site....