MPS returned to Westminster on Monday – but there had already been a tumultuous start to the year with the news last week that the UK’s ambassador to the EU, Sir Ivan Rogers, had resigned.

A highly respected and experienced diplomat, he was due to remain in the post for another nine months at least, and to play a key role in the Brexit talks that are expected to begin in the spring – which makes his resignation so worrying.

Sir Ivan was held in high respect by politicians of all sides in both Westminster and Brussels, and his departure at such a critical time is a significant loss for the UK. It raises serious questions about the government’s readiness for Brexit negotiations, and the approach they are taking.

Since the referendum, I and my Labour colleagues have been asking the government to set out the basic terms of their negotiating stance. It was only after a vote on an opposition motion in December that they finally committed to publish a plan outlining the basic terms of Brexit before Article 50 is invoked.

The prime minister has set a March 31 deadline to trigger Article 50, with a real possibility that it could come sooner – yet in his resignation email to colleagues, Sir Ivan wrote that: “We do not yet know what the government will set as negotiating objective for the UK’s relationship with the EU after exit.”

That the UK’s ambassador to the EU, who would be expected to be central to the negotiations, should be without such crucial basic details at this stage is absolutely astonishing and deeply concerning.

Time is running out, and the government must demonstrate that they actually have a plan - and a clear timetable for publication which, as we in the Labour party have repeatedly made clear, must allow for proper scrutiny by the House of Commons, the devolved administrations and relevant Select Committees.

We are entering into one of the most important political periods in living memory for the UK, yet the government has clarified nothing. This is just one of the reasons I was not prepared to vote to support the PM’s arbitrary timetable for activating Article 50.

I and colleagues are going to continue to hold the government's feet to the fire, and I have secured a parliamentary debate on the impacts for Welsh Infrastructure of Brexit next week – with projects like the South Wales Metro top of my concerns.