Jo Johnson and Stephen Kinnock argue for and against an alternative Brexit option.
The public should be given a say in whether they want Brexit to proceed, says Jo Johnson MP.
The government is asked about the impact of the resignations of Jo Johnson and brother Boris.
Jo Johnson MP says it would be a "democratic travesty" if the public were not consulted again about Brexit.
Jo Johnson called for a fresh referendum as he resigned as transport minister over the Brexit deal.
Transport minister Jo Johnson has told the House of Commons that since the introduction of a third new timetable on Sunday, Govia Thameslink Railway (GTR) passengers are seeing more services every day and on-the-day cancellations have "significantly reduced".
He was responding to an urgent question from Shadow Transport Secretary Andy McDonald on the performance of the Govia franchise since the introduction of the first new timetables on 20 May which caused delays and cancellations.
Mr Johnson said that the public performance measure - which shows the percentage of trains that arrive at their terminating station within five minutes - had improved on the Thameslink line, closing at 84% on Tuesday and at 86% for Great Northern Services.
He added that all timetables take time to bed in but "the department is closely monitoring [GTR] for sustained performance improvements".
Mr McDonald said the government must "stop pussyfooting around and strip Govia of their contract without delay", to which Mr Johnson said the department was looking at whether GTR had breached its contracts and the government "won't hesitate to take tough action against them if they are found to have been at fault".