Decommissioning Sellafield nuclear plant is not happening fast enough, and could add further costs to a project that is already estimated to cost £136bn, MPs have said.

A report from the Public Accounts Committee (PAC) found that Sellafield Ltd has missed most of its annual targets for retrieving waste from several buildings on the site, including the Magnox Swarf Storage Silo (MSSS).

The MSSS has been leaking radioactive water into the ground since 2018, amounting to roughly an Olympic swimming pool’s worth every three years. While the Nuclear Decommissioning Authority (NDA) accepts that the leak is the “single biggest environmental issue” at Sellafield, it said that the radioactive particles are “contained” in the soil and do not pose a risk to the public.

Sellafield, on the coast of Cumbria, began operating as a commercial-scale nuclear power station in 1956. Energy generation at the plant stopped in 2003, but the painstaking decommissioning process typically takes decades and presents...