The Government has confirmed that a number of promises it made in its manifesto at the General Election may be broken if voters quit the EU.
The Conservative Manifesto pledged to reduce income tax for 30m people during the 2015 General Election however the Prime Minister's spokesperson has said finances would need to be reconsidered to cope with life outside the EU.
During Prime Minister's Questions David Cameron backed Chancellor George Osborne's announcement that they would have to implement an emergency Budget this year to cope with the £40m black hole in Treasury finances that would be left by Brexit.
The spokesperson for the Prime Minister said: "The situation you've got here is the most respected and impeccably independent bodies like the National Institute are warning very clearly that because of the economic shock and potential recession that would follow that by 2020, you would have a £40bn black hole in your public finances.
"That is something that needs to be addressed. That has to be dealt with."
"It's not an optional issue here.
"We made clear manifesto pledges we would want to keep but we also set out very clearly today the very serious impact leaving the EU would have and by 2020, which is the end of this Parliament any Government that is drawing up its plans for the coming years in the new manifesto - you are going to have a £40bn black hole in the public finances.
"If we vote to Remain in, we will deliver those and will continue to grow. If we vote to leave, by 2020 when those new manifesto pledges are drawn up, there is clearly a risk."
"It's very important that people do not go into the polling booth and make a decision, then weeks, months later, say well no-one told me about the huge economic shock that was coming.
Asked whether the Government would raise income tax during this Parliament, the Prime Minister's spokesperson, said: "Hopefully if we vote to Remain we won't have to."
Speculation that an emergency budget would not receive the backing within Parliament to pass, the spokesperson said he would not engage with discussions on the mathematics of a potential vote.
Vote Leave have said 57 MPs would not support an emergency budget.
He said: "I will leave the prediction games to the experts. What we are saying is we have a very clear warning there would be a huge black hole in the Government's finances. The Government then has a choice. You either address that black hole and take action to tackle it, or you don't, and you send your economy into distress. That is the cold reality."
Splits among the Remain campaigners also emerged today as Labour say they would not back the emergency budget if it involved austerity cuts.