The Government should introduce legislation to make lying in the House of Commons a criminal offence. This would mean that all MPs, including Ministers, would face a serious penalty for knowingly making false statements in the House of Commons, as is the case in a court of law.
But even in that situation they would be accused of lying, so it would have to be investigated. It would massively chill speech.
Given the alternative of having them make outright lies, i.e. regarding the benefits of Brexit? I’m OK with that