Your code looks right to me. It's just that the module itself is b0rked. The most recent version of the module was released in July 2001. It attempts to read data from a website that was acquired by Microsoft and shut down in 2002.
If you only need UK data, take a look at these:
In reply to Re: WWW::MapBlast module
by tobyink
in thread WWW::MapBlast module
by maheshkumar
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