Parliament should scrutinise the negotiations, including those about trade, on the UK's withdrawal from the EU, the House of Lords has said.
The Lords EU Committee has said the withdrawal process is arguably the “most important task that the government has undertaken since the Second World War”, and all aspects should be effectively scrutinised.
In a report, Scutinising Brexit: the Role of Parliament, the committee added that parliamentary scrutiny is necessary to hold the government to account, but also "critical to the success of the withdrawal process, and that this scrutiny will provide an audit trail for future generations".
It said scrutiny is critical to success as ratification of any treaties arising out of the negotiations will require parliamentary approval, while national legislation giving effect to the withdrawal and new relationship will need to be enacted by both Houses.
Chairman of the EU Committee, Lord Boswell, said: “In this report we conclude that it’s vital that Parliament is involved in scrutinising every step of the withdrawal process, including any informal discussions that may precede Article 50, formal negotiations under Article 50 itself, and any continuing negotiations establishing a new relationship between the UK and the EU.
The negotiations are of immense significance to the future of the UK. The rights of EU and UK citizens currently living in each other’s countries, our internal security, and the long-term prosperity of the UK are all going to be shaped by these negotiations.
"We can’t afford to get this wrong, and we urge the government to ensure that effective scrutiny is placed at the heart of its plans."
The report added that "it is inconceivable that [the negotiations] should be conducted without effective parliamentary oversight. It follows that full parliamentary involvement throughout the negotiations will ultimately assist the government itself, as well as being in the public interest."
The Lords stressed that withdrawal negotiations should take place in the knowledge, at the very least, of the likely shape of the UK’s future relationship with the EU.
The report also said that the fact Article 50 won't be triggered by the end of the year raises the prospect that informal negotiation could take place.
"Although it currently seems unlikely that the European Commission (which is formally responsible under Article 50 for conducting negotiations on withdrawal) would contemplate participation, the government may try to agree a common approach to a number of key issues in discussion with the other Member States (who, as the European Council, would be responsible for agreeing a negotiating mandate for the Commission)," it said.