It's P.O. Box 272 in this post office. I guess he does this so that people can't easily find out his home address.
The post office was fortuitously easy to find: Open Google Earth. Paste in Cobham, Surrey KT11 2FQ, England, U.K. Zoom in to street level and choose a 360 degree lookaround view. The post office is practically right there. It's interesting to do, because it puts the post office in context. You can get other views of it than the one I've shown.
I'm still looking for his house. (I have an old Surrey address of his, not so interesting.)
محمد النشائي All El Naschie All The Time محمد النشائي