Miliband was asked to speed up delivery of mini nukes after Labor delayed selecting the designer.

Ministers have been urged to continue building mini nuclear reactors in the UK after the launch was delayed again.

Yesterday the Government delayed a decision on selecting a company to develop the new technology, in a blow to Britain’s nuclear ambitions.

The latest setback comes amid fears the UK could be left behind in the global race to pioneer mini nuclear power plants.

Energy Secretary Ed Miliband was accused of “kicking the can down the road” after the process was delayed.

Mini nuclear reactors, or small modular reactors (SMRs), are cheaper and faster to build than full-size nuclear power plants and are seen as critical in the drive toward net neutrality.

Ministers will choose the winner of a long-running SMR design competition in the spring. A decision was expected by the end of this year but was delayed in part because of the general election.

A shortlist of four companies, including British engineering giant Rolls-Royce, will be invited to negotiate with government agency Great British Nuclear. They will then present final offers to be evaluated by the Government.

Tom Greatrex, director of the Nuclear Industry Association, said: “While it is good to see the competition reaching this stage, the critical thing is to reach a decision as soon as possible without further delays to the now published timetable.”

‘Confidence in the UK Government’s pronouncements on support for SMRs depends on meeting the commitments made today. “It is vital for confidence in the supply chain, as well as driving broader nuclear ambition.”

A Rolls-Royce spokesman said: “We have been calling for pace for several years and have seen recent examples of decisions being made quickly.”

It has made progress in other European countries (including Sweden, the Netherlands and the Czech Republic) advancing SMRs.

And Silicon Valley giants Amazon and Google recently announced investments to develop the technology.

Conservative energy spokeswoman Claire Coutinho said: “It appears that SMRs are good enough for Google, Amazon and the Czech Republic, but not for Britain under the Labor Party.”

Ed Miliband’s slow pace on nuclear means he has neglected a cheap and reliable source of energy.

There was nothing new in this budget for nuclear energy except delays. This is a disaster for growth and for our energy security.’

The American-Japanese alliance GE-Hitachi and American companies Westinghouse and Holtec are also participating in the competition announced in 2015.

But it was not until 2023 that Great British Nuclear began the design race. Six contenders were announced in October, but French company EDF withdrew from the race and American company NuScale was eliminated in September.

A Department of Energy spokesperson said: “There are now four companies shortlisted in this tender and, as confirmed in the budget, Great British Nuclear has commenced contract negotiations.”