One vision of the UK’s future involves a decarbonised economy powered by clean, renewable energy. Another involves making the UK an AI superpower.

The government departments responsible for these two visions do not appear to have agreed on their numbers.

The Department of Science, Innovation and Technology (DSIT) thinks AI datacentres will consume 6GW of electricity by 2030. The Department of Energy Security and Net Zero (DESNZ) appears to think they will use less than a tenth of that.

Tim Squirrell, the head of strategy for the NGO Foxglove, said: “The government’s cluelessness over the environmental impact of datacentres would be laughable, if it weren’t so alarming.”

Cecilia Rikap, a researcher at University College London, said: “There are two ways to interpret this ‘misalignment’: either DESNZ and DSIT are incompetent, or there’s some kind of magical thinking about AI and big tech. Either way, the episode uncovers how these corporations control not only the AI value chain, but also the UK government.”

DESNZ is responsible for the UK’s carbon budget growth and delivery plan, which sets out how the government will reach its international climate targets.

In January, Foxglove filed an environmental impact assessment request with the department, asking how it had incorporated AI datacentres into its projections for Britain’s emissions. In response, DESNZ referred researchers to its broader forecasts for the energy use of Britain’s “commercial services” sector, and said it did not hold separate projections for datacentre growth.

The forecasts appear to project that the energy use of the entire sector will grow by 528MW between 2025 and 2030 – equivalent to adding the consumption of 1.7m homes by the end of the decade.

This projection is 10 times lower than the amount of electricity the government has committed to AI datacentres as part of its UK compute roadmap. That policy paper, put forward by DSIT in 2025, sets out a “bold, long-term plan to transform our national compute ecosystem” by building AI datacentres.

It adds: “We forecast that the UK will need at least 6GW of AI-capable datacentre capacity by 2030.”

This will come from multiple AI growth zones – hubs across the country where the government is attempting to attract investment into datacentres. Each would require at least 500MW of electricity – an amount only slightly less than DESNZ’s forecast for the increase in energy usage of the entire commercial services sector.

It is unclear how the discrepancy between the two departments’ forecasts arose. But one day after the Guardian requested comment from DSIT and DESNZ, DSIT appears to have revised its figures published on its website for the total emissions of the AI datacentre sector, raising them more than a hundredfold.

Originally, DSIT’s projections for the carbon emissions of additional AI computing capacity were between 0.025m and 0.142m tonnes of carbon equivalent (MtCO₂) – below 0.05% of Britain’s projected emissions. These figures were in an annexe to the compute roadmap.

Earlier this year, that document was removed from the government website after Carbon Brief raised questions about the plausibility of the figures. On Thursday, after the Guardian asked about them, DSIT updated its numbers.

In a statement posted online, it said: “The UK’s cumulative 10-year greenhouse gas emissions from AI compute could range from 34 to 123 MtCO₂ – this is around 0.9-3.4% of the UK’s projected total emissions over the 10-year period.

“If successful, the UK’s grid decarbonisation plans would help to reduce emissions from datacentres towards the bottom end of this range,” it added.

A spokesperson for DESNZ said: “datacentre emissions are factored into our modelling, including for carbon budget 7,” adding: “The AI Energy Council is exploring opportunities to attract investment and support the development of clean power for datacentres.”

Carbon budget 7 is to be released this summer. A spokesperson for DSIT referred the Guardian to DESNZ.