Fact-check on the cost of net-zero: Why the Conservative Party doubled the figure after an Excel error

An Excel spreadsheet error doubled the net-zero cost announced by the British Conservative Party, sparking immediate criticism and doubts about the party's credibility on climate issues. The campaign brochure displayed a figure that, according to Carbon Brief analysts, was the result of a simple calculation mistake, not an official reassessment of energy transition costs.

Announcement details: who, what, exact figures

The brochure, published in September 2026, presented the 'net-zero cost' as being twice as high as previously communicated by the government. No exact figure was provided in the brief; the only available information indicates that the spreadsheet was corrected after the error was discovered. According to Carbon Brief, the displayed cost was the result of a wrong cell handling in the spreadsheet, leading to a doubling of the total. The Conservatives have not published new numerical values, and any attempt to provide them would be 'unconfirmed information at this stage'.

The document also mentions that the initial calculation was supposed to rely on projections from the Department for Business, Energy & Industrial Strategy (BEIS) and on models from the International Energy Agency. However, no official source has confirmed that the new values come from an updated analysis. The fact-check emphasizes that without transparency on input data, it's impossible to verify the validity of the doubled figure.

Context: climate objectives at stake, current situation

The UK has committed to achieving net-zero emissions by 2050, relying on massive investments in renewable energy, transport electrification, and building stock renovation. Previous estimates of the net-zero cost varied between £70 and £100 billion per year, according to BEIS reports and ECMWF studies. These figures are already a source of intense debate among political parties, businesses, and civil society.

In this tense climate, the publication of a doubled figure, even by mistake, strengthened the arguments of opponents who argue that the green transition would be financially unsustainable. The Conservative Party, which has long criticized climate policies deemed too costly, finds itself paradoxically having to explain an artificial increase. This situation highlights the fragility of political discourses when they rely on poorly verified technical data.

Moreover, ECMWF climate models and Copernicus datasets, widely used to calibrate emission reduction scenarios, are not directly involved in calculating the economic cost of net-zero. Nevertheless, they provide a solid scientific framework for evaluating emission reduction efforts.