May sought to reassure her audience that she is determined to avoid changes to the Irish border, which is now invisible.
The statement came when Javid was dismissing newspaper reports that Downing Street strategists were considering holding a snap general election on June 6 if British Prime Minister Theresa May can not get her Brexit deal through parliament before the Brexit deadline of March 29.
He was backed by the former Conservative Brexit minister Steve Baker, who tweeted that the prime minister should "expect a further substantial defeat" if she fails to remove the backstop altogether.
"Parliament's mandate is to replace the backstop, the current backstop.is toxic to those of us living in Northern Ireland".
But she said that the Withdrawal Agreement can not be renegotiated, so questions about the border would have to be addressed in the Political Declaration on future EU/UK relations.
Britain is scheduled to leave the European Union in less than two months' time on 29 March.
Ms May acknowledged that there are concerns amongst nationalists in Northern Ireland about their rights post-Brexit - and that Northern Ireland voted to remain - but promised unequivocally that she will "not allow a return to a hard border" in Northern Ireland.
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"These emergency evacuation plans have been in existence since the Cold War, but have now been repurposed in the event of civil disorder following a no-deal Brexit", a UK Cabinet Office source was quoted as saying in the report.
The row comes as the prime minister sets up a new committee of Conservative MPs created to work on "alternative arrangements" to the backstop.
The comments came as Justice Secretary David Gauke became the latest Cabinet minister to suggest that Brexit might have to be delayed beyond the scheduled date of March 29.
Mrs May is now seeking new tweaks to the negotiated deal which was voted down by the House of Commons last month.
Keen to avoid the economic disruption a no-deal Brexit would bring to Germany's economy, which slowed sharply past year, Merkel also values Britain as a like-minded partner and wants to keep its security expertise close at hand.
As a way to prevent a hard border, Brussels and London agreed a so-called backstop - basically a promise that unless the sides come up with a better idea then the United Kingdom would remain bound by European Union market and customs rules so that goods would not have to be checked.
The prime minister also floated the prospect of a joint UK-Ireland World Cup bid for 2030 and said that "the ties of family and friendship between the UK and Ireland are more important than ever". The group was holding three days of meetings with ministers and civil servants to investigate possible changes to the European Union divorce deal, which was rejected by Parliament last month. The EU is looking to protect its single market and has said the backstop would only be a temporary arrangement.
"In my own department I have got Border Force and I asked Border Force months ago to advise me to look at what alternative arrangements were possible".