The new Metropolitan Police maps are based on areas that are described in the press release as:
Crime mapping areas are based on pre-defined (‘sub ward’) areas consisting of an average of 633 households. There are 4,765 ‘sub wards in London.
These ‘sub-wards’ are in fact Super Output Areas (SOAs) which have been defined by National Statistics for applications based on neighbourhood statistics. More precisely, the maps use the (catchily named) Lower Layer Super Output Areas, or LSOAs.
National Statistics very helpfully make boundary data for these areas freely available on their website, and will also send them to you on a CD-ROM for free if you prefer.
This is all good stuff… except that if you want to add your own data to existing sets based on these boundaries, you really need a postcode to SOA lookup table. And this is apparently not free but can only be done if you have access to commercial packages such as the Ordnance Survey’s Code-point.
If anyone knows of a free postcode-SOA lookup file then please let us know as this would be really helpful for data-mashers. If indeed a free version of this does not exist as yet then this is a priority dataset for us to try to make available.
Richard Allan, Task Force Chair
Power of Information Task Force 
You might try here: http://www.statistics.gov.uk/census2001/product_pc_headcounts.asp
Free only on cd.
I haven’t tried it but I believe that ONS published a list of postcodes current to the night of the Census. In the file it contains the postcode, population and output area (from which you can generate the SOA).
Obviously this is some way out of date, but can be used reliably for 2001 datasets. For more recent data this could be a starting point.
Hope this helps.
Can’t this be done using the SOAP API (and a few calls) from NeSS?
It’s far from good, but it might get the job done.
Failing that, a this and do a regexp on the html you get back.
given how fast that would be to do, it might be far easier than doing a SOAPy dance.
Thanks for the helpful suggestions which I’ll look into. It’s especially interesting that Neighbourhood Statistics is exposing a postcode to LSOA lookup for website users. Wondering now whether National Statistics, who generally release their date freely to the world, can make available the lookup table from Neighbourhood Statistics as they do with the datasets it offers…
I’ve asked the NeSS people whether their postcode data is from 2001, or more recent.
I make good use of the Census OA data for the backend processing for FillThatHole, it’s very useful data. Perhaps one day we’ll have the equivalent of the US TIGER/Line database in the UK?
The answer is that NeSS uses up-to-date postcode data: “the postcode data used by the Neighbourhood Statistics website is updated
on a quarterly basis using data supplied by the Royal Mail. The last time
the postcode data was updated was in August 2008. Please see
http://www.statistics.gov.uk/geography/nspd.asp for more details.”
Pingback: A Good Postcode Summary « Power of Information Task Force