The Chancellor has signed a landmark nuclear accord with the United States, promising to deploy small modular reactors (SMRs) to power 10 million British homes by the end of the decade. This deal, announced with fanfare from Downing Street, is being hailed as a triumph for energy security and a clean break from volatile fossil fuel markets. But let us not get carried away by the headlines. The bottom line is simple: this is a massive fiscal gamble, and the market will be watching the delivery timeline with hawkish eyes.

An SMR is essentially a scaled-down nuclear reactor, theoretically cheaper and faster to build than traditional gigawatt-scale plants. The US is a leader in this technology, and the accord opens the door for US firms like NuScale and GE Hitachi to partner with UK entities. The goal is to have a fleet of reactors operational by 2030, generating roughly 10 gigawatts of capacity enough to power a third of Britain's homes. The price tag: an estimated £20 billion in public and private investment, with the government extending a generous subsidy regime to guarantee a strike price for the electricity produced.

Now, the optimists say this will turbocharge the UK's net-zero ambitions, reduce reliance on imported gas, and create a domestic supply chain for nuclear components. The Treasury is keen down a new growth sector with thousands of high-skilled jobs. But let us examine the ledger. The history of nuclear power in Britain is littered with cost overruns and delays. Hinkley Point C, the only new large reactor under construction, is billions over budget and years behind schedule. To assume SMRs will magically avoid these pitfalls is to ignore the structural inefficiencies of the construction supply chain and the planning quagmire.

The financing model is also a cause for concern. The accord relies on a regulated asset base (RAB) model, where consumers pay upfront through their bills before the plants generate a single watt. This is effectively a tax on households, and with inflation still stubbornly above target, it risks fuelling inflationary pressures further. The Bank of England will be watching gilt yields nervously. If the market perceives this as another unfunded fiscal expansion, we could see a rise in long-term borrowing costs, a form of tax on future growth.

Moreover, the 2030 deadline appears ambitious to the point of fantasy. Even the most optimistic timeline from the industry suggests first-of-a-kind SMRs will take at least seven years from final investment decision to grid connection. That pushes operability to 2028 at the earliest, with broader deployment by the mid-2030s. The government has a habit of making bold promises about energy infrastructure only to miss them by a wide margin. Remember the smart meter rollout? The high-speed rail? The market is not stupid; it will price in this risk from day one.

Capital flight is another risk. The nuclear accord ties Britain's energy policy to US technology and supply chains. In a world where trade tensions are rising, any disruption to US exports could leave the UK exposed. And let's not forget that the US itself is struggling to deploy SMRs commercially; the first US SMR project, the Carbon Free Power Project in Idaho, was cancelled in 2023 due to cost overruns. Why should we expect better outcomes 3,000 miles away?

But to be fair, there is a case for cautious optimism. The accord includes substantial domestic manufacturing requirements, which could support British engineering and create a skills base. The Department for Business and Trade calculates that each gigawatt of nuclear capacity supports 10,000 jobs. If the programme hits its targets, the economic multiplier could be significant. The question is whether the fiscal discipline can be maintained. The Treasury has promised a cap on consumer exposure, but such caps have a habit of being revised upward when costs spiral.

In conclusion, this nuclear accord is a bold bet on a technology that has yet to prove itself at scale. It could be the foundation of a low-carbon power system or the latest in a line of expensive white elephants. The market will judge the government's ability to deliver. For now, the smart money is watching the gilt curve and inflation expectations. If those stay calm, maybe the reactors will too. But I would not bet the house on it.