Energy minister Michael Fallon and Green Party MP Caroline Lucas had a nuclear war of words in front of an influential group of MPs.

The pair had a long debate about the definition of the word "subsidy" while Fallon took evidence from Energy and Climate Change Committee in the House of Commons about, among other things, the UK government's agreement with EDF to build a new nuclear station at Hinkley Point in Somerset.

The French firm will earn at least £92.50 a megawatt-hour over a 35 years at the site.

If EDF goes ahead with a second nuclear project at Sizewell in Suffolk the strike price will fall to £89.50.

The government will also offer loan guarantees to help 65% of the cost of construction.

The heated exchange, which lasted more than 10 minutes, erupted after Lucas claimed that the government had used "a sleight of hand" by redefining the original coalition agreement that there would be no public subsidy for new nuclear energy in the UK.

Lucas stressed "no public subsidy means no public subsidy". She argued that the government had changed the pledge to mean "no subsidy unless it's being made in a similar way to other energy sources".

Fallon dismissed the charge and said that the government told parliament in October 2010 that there would be no levy or direct payment or market support for "new nuclear that wasn't available in a similar to any other low-carbon new type of technology".

"I'm an English graduate and one thing that really annoys me is when people redefine words," Lucas responded. "A subsidy doesn't cease to be a subsidy just because it's offered to more than one source, does it?"

Fallon said: "If you're trying to get somebody else to put up £16bn worth of money to build a nuclear station and to accept all the construction risk in doing it, you obviously have to offer them some degree of reserved access to the grid when they start supplying electricity to it.

"So, there's a support mechanism for nuclear just as there is to offshore wind or biomass or anything else.

"These are market-based support mechanisms designed to facilitate the earlier introduction of high-cost, low-carbon technologies that the market wouldn't otherwise have been able to finance as quickly as we need them," Fallon stressed.

Lucas nearly cornered the Conservative MP when she argued that the fact that the government has to submit an application for state aid clearance to the European Commission for a new nuclear power plant "surely means it's a subsidy".

Fallon attempted to slap the accusation away by stating that "lots of support mechanisms have to go through the European Union".

Zac Goldsmith, Conservative MP for Richmond Park, momentarily intervened in the tussle and backed Lucas by asking Fallon to restate his definition of subsidy, but the minister was unwavering and maintained that the nuclear agreement does not involve subsides.