Since the sale of several of the gas distribution networks in 2005 it has not been appropriate for National Grid to report on gas demand by postcode.  Responsibility for this has been taken over by the Department for Business, Enterprise and Regulatory Reform (BERR).  Statistics for energy consumption by region are available on the BERR website.

http://www.berr.gov.uk/whatwedo/energy/statistics/regional/regional-local-gas/page36200.html