What are you trying to do? If you use the geo.places table getting information for London, England (or actually anywhere in the world) is as simple as
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select * from geo.places where text="london,uk"
This also works with postcodes, for example my flat:
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select * from geo.places where text="n42xx"
It seems to me your problem is that you are trying to access the authenticated endpoint of YQL whilst what you really need is the public one:
click here to see the result of the above query