From my experience (in North West England) having worked many contracts in both the private and public sector, I'd say there are far fewer than one in five computer programmers is female; I'd guess it was closer to 1/15.

Of course, and this is all completely anecdotal, but at my first job after university (at a medical data company), there was only one woman in the 'software' section, and about 70 men.

It's a pity.