Downing Street said David Cameron was ready to "listen to the arguments" about a ban on smoking in cars that are carrying children.
The Prime Minister's official spokesman told a media briefing, "This is an issue that is going to be discussed and debated in Parliament today, and the Prime Minister's view is that he wants to listen to the arguments."
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"My sincerest apologies to everyone who purchased tickets and were planning to come to the upcoming shows."
His comments at the Defence and Security Forum on Monday came after a £20 billion black hole in the budget for the next decade emerged.
The Foreign Secretary said he thinks the health service should be "at the very top of the list" for a windfall after the UK leaves the EU.