Search for address from postcode

I'm having a play with Nominatim, and trying to glean addresses from postcodes. If I search for a full address (as in the example on the wiki page), this works fine:

http://nominatim.openstreetmap.org/search?q=135+pilkington+avenue,+birmingham&format=json&addressdetails=1

However, if I just search for the postcode, I expect get back houses that contain the postcode as well as postcodes, but, as it stands, I just get postcodes:

http://nominatim.openstreetmap.org/search?q=B72%201LH&format=json&addressdetails=1

Is there any way round this? Or am I doing something wrong?