Cameron's announcement of a 'right to data' is welcome – but he must also ensure that taxpayer-funded data is open to all

From the safety of long opposition, few political promises are easier to make than pledging to open up the flow of information from the government machine once you gain power. But the ease of such promises, and their history of being watered down in office, is no reason to dismiss the "setting data free" comments in David Cameron's speech on civil liberties on Thursday. The three-year-old Free our Data campaign – founded by myself and the Guardian's technology editor Charles Arthur – will welcome Cameron's re-stated promise to publish every item of government spending over £25,000 and raw data to allow communities to build their own crime maps and councils' performance data in a standard format.

At the risk of upsetting the Guardian's commercial folks, I'm personally also in favour of Cameron's plan to publish all public service vacancies "online and in a standardised way".

We will cheer most loudly at the plan to create a new right to data and proactively to identify the 20 most useful data sets on public services and make them available for web mash-ups.

Now the caveats. Although the Cameron promises are welcome, and given the current state of the polls, in harder currency than most opposition bright ideas, they appear to go no further than current government policy on the most contentious issues faced by the free data campaign. These emerge when taxpayer-funded data has value for commercial rather than political purposes, and, most crucially, where the state itself exploits this potential.

Over the past three years, promoting the Free our Data campaign in the Guardian's Thursday technology section, on our blog and in numerous conferences, debates and other public meetings, we have found near unanimous support for making (non personal) data available to citizens. Controversy begins, however, when things get commercial: if someone finds a way of making millions out of state-funded data, shouldn't the state take a cut? We would say no, both on principle – free should mean free – and for the practical reason that a regime to monitor re-use and collect royalties would cost huge sums to run and function as a bureaucratic barrier to entrepreneurialism. We are surprised that the Tories, of all people, don't seem to have got it – yet.

Life gets even more complex when the government itself is operating in this market. A generation after a Tory government got the state out of the business of running telecoms and building ships, nationalised industries rooted in monopoly relationships with data suppliers remain at the forefront of the knowledge economy. The most controversial of these is Ordnance Survey, whose core public task of maintaining an accurate geographical database of Britain is hopelessly entwined with the commercial pressures of operating as a "trading fund". We believe the effect is detrimental to the fast-emerging market in commercial geographic information – and to the efficient running of public services, which, incredibly, are denied free access to Ordnance Survey's core data.

Under its power of information programme, the government has already made some moves towards opening up Ordnance Survey's databases, but has shied away from radical reform of the business model. The Free our Data campaign proposes that this would involve defining Ordnance Survey's core task, funding it from general taxation, and opening the databases thus maintained to all comers, whether public bodies or private entrepreneurs.

To judge by Cameron's speech, which makes no mention of the government's single largest data business, the Conservatives share this aversion to reform. The suspicion must be that the Tory solution is to try and sell off the mapping agency lock stock and barrel. Yet locational information is an essential component of nearly every public data set. To commercialise its supply would be to move in the very opposite direction of setting our data free.