I have a twin currently studying abroad in London at the moment and as a birthday present I wanted to buy a board game from amazon.co.uk. Problem is, the postcode, county and even city name she sent is not being accepted as valid by amazon for some reason I can't figure out.

I have used www.royalmail.com and only come up with the same postcode as she provided, yet it still won't accept it. The details I've given so far it won't accept is as follows:

Town/city: London
County: London
Postcode: N1 6HG

The building she lives in is Alexander Flemings Hall and is in Hoxton Market. Is there some arcane bit of knowledge only known to locals that i'm missing or something else? Help would be grately appreciated :)