Ian Powell, chairman and senior partner of PwC  said in early reaction: ‘The UK’s decision to leave the EU will have significant implications for businesses and we are already working with our clients and people to support them as those implications are understood.

‘History has taught us that UK business is adaptable and innovative when confronted with new challenges and opportunities. There will be significant uncertainty over the coming months as the detailed political and legal issues are worked out, and business confidence may be impacted.’

Steve Varley, EY’s UK chairman, said: ‘We are now entering unchartered territory after the majority of UK voters chose to leave the EU yesterday. It’s the first time a member state has left the union, and this means that the consequences are almost impossible to predict.’

Varley said businesses will need to move quickly to implement short-term contingency plans also starting to plan for the longer term. In many cases, this will include communicating with staff about any potential employment issues that might arise, including the working and travel rights of European and UK employees.

Prime minister David Cameron made an early reference to these issues in his speech following the result this morning, saying: ‘The British economy is fundamentally strong. For Brits living in Europe and for EU citizens living here there will be no immediate change in circumstances and no initial changes in the way people travel, or goods are moved or services are sold.’

However, there will be major changes longer term. Cameron indicated that he will not immediately trigger Article 50, which is the first legal step for leaving the EU. Instead, he signalled the need for a new prime minister who could ‘steer the country to its next destination’. He is remaining in post until then to provide for a period of stability and a ‘steady ship’.

As a result, there will be a leadership battle within the Conservative party, with Cameron indicating this would need to be resolved by the party’s conference in October. The new prime minister would then be in charge of the negotiations to leave the EU.

Varley said: ‘Leaving the EU could also have repercussions for government policy in the coming months. For example, will the government support certain sectors through subsidies or tax relief? With changes to tax policy possible, companies need to consider their current tax profile and how any new tax policies could affect their holding and financial structures.

‘One thing is certain: Brexit will result in a number of large-scale changes for UK plc, in areas such as trade, employment, regulation and government policy. Few changes are likely to happen overnight. As a result, businesses now have a prime opportunity to take proactive steps to prepare for the challenges and opportunities that lie ahead.’

Andrew Sentance, senior economic adviser at PwC, described the UK leaving the EU as ‘potentially a big leap into the unknown’ and said it would be very important for the government to act quickly to resolve the inevitable uncertainty.

‘The EU is a vital market for exporters so it will be important that we secure access to that market in any future settlement with the EU. I would expect that most businesses in the UK want us to keep a close and positive relationship with the EU even if we are not a full member. That could be done by remaining a member of the European Economic Area, or by securing our own specific trade relationship like Switzerland, though this second route is likely to take much longer and be more difficult to negotiate,’ Sentance said.