Prime Minister Theresa May told rebels in her divided party that if they torpedoed her Brexit deal then the UK would leave the EU without any agreement.
Meanwhile, the IMF has said it will make the country much poorer.
The UK is due to leave the EU on March 29 and yet little is clear.
So far, no full exit agreement has been reached and some rebels in May’s Conservative Party have threatened to vote down a deal if she clinches one.
The fate of May’s government and her Brexit plan is in doubt because it is unclear whether she can command the 320 votes she needs in the House of Commons, the lower house of the British parliament, to approve a deal.
“I think that the alternative to that will be not having a deal,” May told BBC TV.
She added that she was confident of getting a good agreement she thought parliament would ultimately approve.