Northern Ireland secretary Karen Bradley has told MPs there will be no return to a hard border, despite a leaked letter from Boris Johnson saying it was not the responsibility of British ministers to prevent one.

Ms Bradley told the Northern Ireland Affairs Committee at Westminster that the Conservative government stood by the commitment it made to the EU last December to avoid a hard border regardless of the outcome of Brexit negotiations.

“The British government stands resolutely behind the joint report from December. There is no change in position with regards the joint report, and also no change in our position with regards support for the Belfast Agreement. We are resolutely behind that,” she said. “That means there will be no hard border. We have said that, the Irish Government has said that and the EU has said that.”

Ms Bradley said her government was working towards an overall UK-EU agreement that means there is no hard border, no new physical infrastructure at the border, and frictionless movement of people and goods.

In a letter to the prime minister, which was leaked to Sky News this week, Mr Johnson said it was not the government’s task to maintain no border but ministers should try to stop it becoming “significantly harder”.

Use the border issue

The foreign secretary said on Wednesday that the letter had been quoted selectively, adding that some in the EU were trying to use the border issue to keep Britain in the customs union.

“What is going on at the moment is that the issue of the Northern Irish border is being used quite a lot politically to try and keep the UK in the customs union - effectively the single market – so we cannot really leave the EU. That is what is going on,” he said.

Mr Johnson left the Commons chamber to Labour cries of “coward” as a debate on his intervention on the border began. Labour’s shadow foreign secretary Emily Thornberry said the letter showed that Mr Johnson was insincere when he said that a return to a hard border would be unthinkable.

“Contrary to the foreign secretary’s previous statements, he accepts that there will have to be changes to the current border arrangements, and he accepts there will need to be border controls that do not exist at present; the only debate is their degree of hardness. But surely the foreign secretary has learned by now that you cannot just be a little bit pregnant: either there is a border or there is not,” she said.