This will probably only be available to listen to again until this Saturday. Here is the link:
http://www.bbc.co.uk/iplayer/episode/b00pn34v/iPM_09_01_2010/
The letter is read out by a woman called Mavis Hyman who has set up a charity. If you press the play arrow symbol and then move the little marker to 7cm along the line marking the time of the recording you should find just the right spot.