On 29 March 2017, Sir Tim Barrow, the UK’s permanent representative in Brussels, personally handed over a letter, signed by Prime Minister Theresa May, to Donald Tusk, the President of the European Council, providing notification of the UK’s intention to leave the EU. This means that the UK Government has officially triggered Article 50 of the Lisbon Treaty, marking the beginning of the formal negotiations to exit the EU.

Today is a landmark on an unknown path into uncharted territory. The process for withdrawing from the EU, which is now officially underway following the UK's formal notification to the European Council of its intention to withdraw, is untested. It is an indication of the challenge ahead that there is no consensus about even the process itself.

The UK Government has stated its intention to agree a new "deep and special partnership" with the EU during the two year period at the same time as agreeing the terms of withdrawal. The EU seems less sure, focused on headline terms of withdrawal, such as budget contributions, and emphasising the protection of its citizens' interests. The notification letter seeks to put the UK's best foot forward in tones of friendship and cooperation and on the basis of shared interests and values, which are not merely economic. Mrs May has sought expressly to link withdrawal terms to the future relationship, emphasising the spirit of continuing partnership in which they should be agreed; in other words, this is not a divorce.

The careful drafting of the letter reflects the wide range of audiences and challenges that the UK Government needs to address, including a nod to the domestic devolution agenda in the promise of a "significant increase in the decision-making power of each devolved administration". The emphasis on early certainty and regulatory evolution will also have been intended to reassure both the EU and address the concerns of many businesses. However, the "detailed proposals for deep, broad and dynamic cooperation" that Mrs May promises to put forward will require all the input they can get.

The task ahead is enormous — or, as Mrs May says, "momentous". Not just for the UK but for the EU and for every member state. For businesses, pro-active engagement with policy makers across Europe will be crucial to understanding the emerging picture and to ensuring that business priorities are understood in return. That is the only way to ensure that your priorities do not become someone else's negotiating compromises.

To learn more, read our earlier blog on what you need to know before Brexit gets underway.