Today, UK Prime Minister Theresa May has officially launched the Brexit progress, triggering Article 50 and starting a two-year countdown before the country exits the European Union (EU).

The key moment was marked by the delivery of a letter signed by May to the Brussels office of European Council President Donald Tusk, notifying him of the UK's decision to leave.

Lawyers from across the profession have been discussing the implications. Here are some of their views:

Jan Putnis, finance partner, Slaughter and May  "There are no big surprises in the Article 50 letter. It is trying to be conciliatory and is notably light on dogma. But it is firm on the government's wish to negotiate a longer-term relationship at the same time as the exit terms. This lays down a challenge to member states to give political authority to the EU's negotiators to discuss those longer-term arrangements."

Gavin Williams, corporate partner, Herbert Smith Freehills "To begin with, there is likely to be a lot of squabbling over what is negotiated when. Key disagreements are likely to centre around any financial contribution from the UK on exit, the framework for and transition to a new trade agreement and the rights of EU and UK expatriate citizens.

"The law is not clear and nor is the means by which any financial obligation could be adjudicated and enforced.  The matter is likely to be resolved by negotiation and the extent to which the UK continues to benefit from EU-funded programmes (eg structural funds and funds for scientific research) and participates in EU programmes following Brexit is likely to play a significant role in the outcome."

Nick Brittain, banking and finance partner, Sidley Austin "We now know that the UK is firmly on the path to Brexit in March 2019, but the service of the Article 50 notice today does not give businesses any level of real comfort on what that path will look like or how they can plan for a post-Brexit future. Although timing is now clearer and the EU Commission has recently been giving more comforting signs on general outcomes of the exit negotiations, the serving of the notice has not clarified or fundamentally changed the UK's ability to predict how Brexit will evolve.

"Whilst some clients have taken precautionary steps to give them flexibility in their reaction to changing trade environment, regulation and UK legislation, there is insufficient certainty at this stage to react one way or another."

Christopher Sullivan, M&A partner, Clifford Chance "While we still don't know what Brexit will look like in terms of the UK's relationship with the EU, we now at least have some certainty on the timescale and schedule. Any form of increased certainty supports boardroom confidence and M&A in general so today's action will have some positive impact, but weighed against that will be the volatility created along the way as negotiations wax and wane.

"Business owners have been a lot less negative about the impact of Brexit than certain economists or political commentators. Whilst questions remain unanswered, vendors' expectations or desire to sell or exit their investments continue undimmed while fundamentals remain strong."

Charles Brasted, public law partner, Hogan Lovells "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 Ms May promises to put forward will require all the input they can get."

Rob Moulton, finance partner, Latham & Watkins "While triggering Article 50 marks the start of the UK's formal negotiations, the starting gun for the financial services industry was fired almost a year ago. The complexity of leaving the EU means that any final decisions about relocation will be taken in 2017, not 2018. The government needs to act quickly to try to secure the necessary 'in principle' commitment to equivalence that will reassure parties that they will continue to be able to carry out pan-European business from London.  Achieving this will not be easy by any means, but making early progress – even if the details are to follow – should be the priority."

Ashley Prebble, insurance partner, Clifford Chance "With two years on the clock until a potential Brexit, insurance companies, whether UK-headquartered or currently benefiting from passporting into UK, simply cannot afford to wait for a deal to emerge before beginning to implement their contingency plans. In the coming months, we fully expect to see more insurers confirming new locations for their EU business and starting to implement the early stages of their plans to ensure that they can continue to serve their clients across the continent."

Deepa Deb-Rattray, real estate partner, Berwin Leighton Paisner  "Triggering Article 50/Brexit has not changed the key issues in the UK real estate – a lot of demand and not enough supply. Hence the new landscape around alternative asset classes such as build to rent, student housing, retirement homes, healthcare and hotels. It will be key for the government to deliver on its promise to invest in key infrastructure and free up public sector land to support more housing supply."

Philip Wood, special global counsel, Allen & Overy  "The best way to secure agreement quickly is for each side to understand the viewpoint of the other side. The most unsatisfactory result would be for the parties not to agree, so that the UK just exits unilaterally. We believe that this might leave the UK and the other nations of Europe embittered and resentful for a generation."

Jonathan Kembery, chief legal officer, Freshfields [On the EU regime for legal services specifically] "It is a response to client requirements for us to be flexible and to work seamlessly across borders. If politicians on either side of the discussion allow our profession to be Balkanised, the damage will be inflicted on the clients whose needs we serve as much as on the lawyers themselves."

Guy Lougher, competition partner, Pinsent Masons "The triggering of Article 50 brings the rules of play for UK business into sharp focus. Brexit will change how businesses deal with customers, suppliers, partners and how they compete with rivals. It will change the fundamentals underpinning business relationships. The bottom line is those relationships will need to change.

"Businesses with critical supply chains have developed them to be highly efficient and resilient within the EU, but they may soon be subject to stresses that they were not designed to withstand. Customer propositions may need to change to take account of new supply chain requirements."

Kieran Jones, partner and head of insurance, Weightmans "UK businesses remain in a state of uncertainty, unable to make any plans of substance for the outcome of the negotiations, though we will see Theresa May's strategy unfold in the coming weeks. Many businesses have started, and should continue, to assess the possible impact of Brexit on their customer base, how they are currently affected by both UK and EU regulation and their dependency on EU-migrant staff.

In particular, businesses should take the opportunity during this period to identify aspects of their operations that are regulated either directly by European legislation or by UK legislation that has implemented EU directives. They should also keep a watching brief for any prospective changes coming down the line, particularly the development of the Great Repeal Bill, which will bring all EU laws onto the UK books."

James Mee, corporate insurance and financial services head, RPC "Many companies have been preparing for this day since the referendum result dust settled. Many are advanced in their thinking as to how to evolve their business models. Much will depend on the outcome of the negotiation – but time is also a factor as businesses cannot leave changes to the last minute. We are already seeing contingency plans being developed at one level or another."

Sunny Mann, trade partner, Baker McKenzie  "What is clear is that there is a stark difference of opinions between the UK and the EU regarding the sequencing of the 'withdrawal negotiations' and the 'future relationship negotiations', and whether they should be conducted concurrently or sequentially. The UK government is clearly pushing for concurrency of the negotiations, stating that talks regarding the UK's withdrawal from the EU should be conducted alongside negotiations regarding the terms of the UK's future partnership with the EU. Conversely, the EU parliament has implied that the withdrawal agreement must precede any talks on the framework for the UK's future relationship with the EU."