Energy Secretary Edward Davey insists that there will not be a direct subsidy of new nuclear, but cannot say the cost will not end up with the taxpayer or consumer.
He says that the Horizon deal with Hitachi is "a real vote of confidence from foreign company" in the UK.
Spades will be in the ground at Oldbury and Anglesey in 2016 or 2017 at the very earliest.
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Rain will affect northern England and Wales later in the day, particularly over the hills. Elsewhere it will be drier but breezy.
The Chancellor will promise to fix a glitch, which means repayments continue to be taken for up to 12 months after the loan is paid off.
The proposal will see the introduction of a discounted railcard for 26-30-year-olds, as the government looks to lessen the cost of living.