rtsp://rmclip1.thny.bbc.co.uk/radio4/comedy/tue1830.ra

(This link works but they haven't put up the link at the BBCR4 comedy
page yet.)

http://www.bbc.co.uk/radio4/comedy/
http://www.bbc.co.uk/radio4/hitchhikers/

You can listen live Tuesdays at 1730 GMT and Thursday 2200 GMT. (times
on the web page are GMT+1)

As to when it will be on BBCWS or your local station that buys
programs from the BBC, your guess is as good as mine.

By the way, if you're having trouble with BBC radio Real Audio listen
again links, try substituting rmclip1.thny.bbc.co.uk for
rmv8.bbc.net.uk. They changed the RA server but not all the .ram
pointers are changed.