I can highly recommend Radio 4 and Radio 4 extra on the BBC iPlayer for spoken word drama and comedy.
If I was to recommend one programme, it would be "Cabin Pressure" by John Finnemore. OK, it's a sitcom, not a drama, but it is a very witty sitcom. It's bound to be repeated on BBC radio at some point, but if you'll take my advice you'll buy it from audiogo.com now anyway.
The six episodes of series one are only $3.99 for all six at the moment.