This link might help...
http://en.wikipedia.org/wiki/BBC_Radio_4#Frequencies_and_other_means_of_reception
DAB & FM signals do not propogate over very long distances - Medium wave 720kHz or Internet are your best chances for a good R4 signal.
see also...
http://www.mwcircle.org/
Good luck...
Peccavi
June 2010