Many of these episodes will be of interest to HN readers. You may need weird methods to listen / download if you're not in the UK.
Landing page: (http://www.bbc.co.uk/programmes/b006qykl)
Antimatter: (http://www.bbc.co.uk/programmes/b00808w8)
Artificial Intelligence 2005: (http://www.bbc.co.uk/programmes/p003k9fc)
Artificial Intelligence 1999: (http://www.bbc.co.uk/programmes/p00545h7)
Asteroids: (http://www.bbc.co.uk/programmes/p003k9kh)
Theories of Everything: (http://www.bbc.co.uk/programmes/p004y24b)
There is far too much to list here.