Just last week Rishi Sunak held a special Downing Street press conference to warn peers not to ignore ‘the will of the people’ and block his Rwanda plan. Fast forward a few days and Sunak’s warning appears to have fallen on deaf ears, with the Prime Minister suffering his first Lords defeat on the topic before the Safety of Rwanda Bill has even begun its journey through the Lords.

This evening peers voted to delay the ratification of the international treaty between the UK and Rwanda, the legally binding agreement signed with Rwanda last month. By 214 votes to 171, peers backed the motion that demands the government delays any deportation flights to Rwanda until agreed safeguards have been put in place and shown to be working.

While the debate on the treaty is separate to the Safety of Rwanda Bill (which peers will begin debating Monday), it is meant to work in lockstep with the planned legislation to get around the problems raised in the Supreme Court ruling that declared the scheme unlawful. The treaty commits both the UK and Rwanda to using new infrastructure and it added legal safeguards to ensure that Rwanda is a safe place to send asylum seekers. However, last week the Lords international agreements committee published a report that said the promised safeguards were incomplete and that ten practical steps must be taken before implementing the policy. The report recommended the treaty not be ratified.

So, how serious a problem is this for Sunak? It’s worth noting that it is unprecedented: it is the first time since the legislation was introduced that the Lords has approved a motion to delay ratification of an international treaty. Yet despite this, peers do not actually have the power to block the ratification, only the House of Commons does. It means the result raises two important questions for Downing Street. First, will the result inspire MPs to object to the treaty? Second, does it suggest that the Lords are likely to object to the Safety of Rwanda Bill too? If the flavour of tonight’s debate is anything to go by, the bill is in for a rough ride when it comes to the House of Lords next week.