Of those businesses who have engaged in discussions, both formal and informal, two fifths (40%) expect EU negotiations to have a negative impact on their business – compared to only 6% who anticipate mainly positive outcomes.

With the clock ticking, the research also highlighted that almost a third of businesses (29%) believe the free movement of goods, services, and capital between the UK and the EU is essential to growth, while one fifth (20%) value access to a skilled workforce from the EU.

Michael Izza, ICAEW chief executive, said: ‘Issues raised within our research – such as access to skilled EU workers and the free movement of goods and services - should be firmly placed on the Prime Minister’s radar when she engages in talks with the EU to ensure the priorities of business are fully considered and complacency is avoided.’

Meanwhile, the latest projections from PwC in its UK Economic Outlook suggest UK GDP growth will slow from 1.8% in 2016, to around 1.5% in 2017 and 1.4% in 2018. While a slow down in consumer spending is a factor, the firm’s analysis also points to the drag on business investment due to ongoing political and economic uncertainty relating to the outcome of the Brexit negotiations.

John Hawksworth, chief economist at PwC, said: ‘There are still downside risks relating to Brexit, but there are also upside possibilities if negotiations go smoothly and the recent Eurozone economic recovery continues. We expect the UK to suffer a moderate slowdown, not a recession, but businesses should be monitoring this and making contingency plans.’

However, Jon Holt, incoming head of financial services, KPMG UK, highlights the need for urgent action by banks, as shown by their responses to the Prudential Regulation Authority’s (PRA’s) request for Brexit business plans.

‘Most of the plans landing in the regulator’s inbox are an outline of options rather than a concrete course of action but, from our discussions, there are two messages coming through loud and clear: an answer on whether there will be a transitionary arrangement is needed before year-end, and for some banks, especially the smaller ones, it simply doesn’t make sense to split their balance sheet in two,’ he said.

Holt went on to warn: ‘The finance sector has been calling for a transitionary period but we still have no confirmation and we’re reaching make-or-break point.

‘If there is no agreement with the EU to extend the status-quo for several years past March 2019, firms need to take action or face a cliff-edge.

‘In some cases getting a licence to operate overseas is taking teams of around 40 people almost five months. With that in mind, the application process will have to start in the first half of 2018 which means decisions need to be made by the end of 2017. If we reach December without certainty on this, I expect to see a lot of companies pushing the button on relocation.’