MPs will vote later on whether to block the UK from leaving the EU without a deal on 29 March, after again rejecting the PM’s withdrawal agreement.
Wednesday’s vote would not rule out the prospect of a no-deal exit later this year, if talks are extended but the UK is ultimately unable to agree a deal.
Theresa May’s deal was defeated in the Commons again on Tuesday by 149 votes.
The EU’s Michel Barnier said the UK must decide what it wanted and the risk of no deal had “never been higher”.
He told the European Parliament the EU had gone “as far as it possibly can” and the proposed exit agreement, rejected by 391 to 242 votes, “will remain the only available treaty”.
Ahead of the no-deal Commons vote, expected at about 19.00 GMT, the government announced that most imports into the UK would not attract a tariff in the event of a no-deal Brexit.
Under a temporary scheme 87% of imports by value would be eligible for zero-tariff access – up from 80% at present. Tariffs would be maintained to protect some industries, including agriculture.