Closest to Blackfriars is probably the Hilton Docklands which is on the other side of the river and is not super close (and not at all close to the tube) You would be probably be better off staying at one of the other Hiltons which though further away will actually allow you to get there quicker because of better tube access.

London has one of the most comprehensive subways in the world so no matter which of the other Hiltons you stay at you should get to Blackfriars quite quickly, under 20 minutes, from say the Paddington.
You could however use the water-taxi from Docklands area to the Embankment, nice 10 min ride (assuming its not real cold)
Mike



[This message has been edited by MIKESILV (edited 02-04-2003).]