Money given to Wales as a result of UK Government spending on the HS2 rail project could add up to an extra £5.3bn on the total bill according to opponents of the scheme. Finance Minister Jane Hutt has acknowledged that the Welsh Government has already received a further £84m from the Treasury.
The funding is known as a 'Barnett Consequential' because it's allocated using the Barnett formula for working out the share of UK spending devolved nations should receive. The move has been welcomed by Welsh politicians for setting an important precedent.
But it's also been criticised by opponents of the whole HS2 scheme who say it adds what the call the spiralling costs of the project.