A campaign to release UK postcode data that is currently the commercial preserve of the Royal Mail (prices at this link) has been gathering pace for a while. And not so long ago in July, someone uploaded a set to Wikileaks.

How useful was this, some wondered: the Guardian’s Charles Arthur, for example.

In an era of grassroots, crowd-sourced accountability journalism, this could be a powerful tool for journalists and online developers when creating geo-data based applications and investigations.

But the unofficial release made this a little hard to assess. After all, the data goes out of date very fast, so unless someone kept leaking it, it wouldn’t be all that helpful. Furthermore it would be in defiance of the Royal Mail’s copyright, so would be legally risky to use.

At the forefront of the ‘Free Our Postcodes’ campaign is Earnest Marples, the site named after the British postmaster general who introduced the postcode. Marples is otherwise known as Harry Metcalfe and Richard Pope, who – without disclosing their source – opened an API which could power sites such as PlanningAlerts.com and Jobcentre Pro Plus.

“We’re doing the same as everyone’s being doing for years, but just being open about it,” they said at the time of launch earlier this year.

But now they have closed the service. Last week they received cease and desist letters from the Royal Mail demanding that they stop publishing information from the database (see letters on their blog).

“We are not in a position to mount an effective legal challenge against the Royal Mail’s demands and therefore have closed the ErnestMarples.com API, effective immediately,” Harry Metcalfe told Journalism.co.uk.

“We’re very disappointed that Royal Mail have chosen to take this course. The service was supporting numerous socially useful applications such as Healthwhere, JobcentreProPlus.com and PlanningAlerts.com. We very much hope that the Royal Mail will work with us to find a solution that allows us to continue to operate.”

A Royal Mail spokesman said: “We have not asked anyone to close down a website. We have simply asked a third party to stop allowing unauthorised access to Royal Mail data, in contravention of our intellectual property rights.”