Leaving the European Union would mean a steep rise in energy bills in the UK and make the country vulnerable to bullying by foreign energy suppliers, Amber Rudd, the energy secretary, is set to disclose as part of the series of warnings being issued by the government over the costs of exiting EU. Rudd will claim in her speech that being in the EU has helped to keep energy bills in check.

However leaving the European internal market would give Britain "a massive electric shock because UK energy costs are likely to sky rocket by at least half a billion pounds a year — the equivalent of British bills going up by around £1.5m ($2.1m) each and every day." The claim is based on a report commissioned by the National Grid. A £500m or more rise in energy bills is equivalent to £20 per household or about one-third less if business consumption is taken into account.

During a visit to an interconnector pipeline in Kent, Rudd will address the employees and speak about the risk of being bullied by "countries such as [Vladimir] Putin's Russia" that "use their gas supplies as a tool of foreign policy," The Guardian reported.

She will reportedly say: "We can't let our energy security be hijacked as a political pawn to bring Europe to its knees. By working together in the European Union each member state can stop this becoming a reality.

"As a bloc of 500 million people, we have the power to force Putin's hand. We can coordinate our response to a crisis. We can use the power of the internal market to source gas from elsewhere. We can drive down the price of imports, as has happened recently in eastern Europe.

"To put it plainly — when it comes to Russian gas, united we stand, divided we fall." However, Matthew Elliott, chief executive of the Vote Leave campaign, termed Rudd's claims "absurd" saying they "aren't backed up by her own research."

"It is quite extraordinary the extent to which the government is willing to do down Britain in its desperate attempt to win the referendum. In fact the EU makes our energy bills more expensive and costs us £350m a week. If we want cheaper bills, less commission interference and the ability to spend our money on our priorities, then the safe option is to Vote Leave," he said.