A majority of British company bosses are looking at quitting the UK following the June vote to leave the EU, a survey out on Monday showed.
Some 76% of 100 chief executives surveyed said they were considering moving either headquarters or operations outside Britain following the 'Brexit' vote.
KPMG said more than half of those interviewed believed the UK’s ability to do effective business will be hindered after leaving the EU.
KPMG UK chairman Simon Collins said: "CEOs are reacting to the prevailing uncertainty with contingency planning.
"For many CEOs, it is important to plan different scenarios to hedge against future disruption."
KPMG said it was aware of international clients who had been considering basing European headquarters in the UK, but had chosen Ireland instead.
It said there was a danger that businesses could start shifting operations abroad with little public attention.
Collins said: "Policy makers should be really concerned about a leaching of British business abroad and should engage with business early to understand what assurances they can offer and closely monitor any shifts overseas.
"Equally, businesses should be sharing their on-the-ground experiences to convene a unified voice into government.”
Lloyd's of London told Reuters last week that the insurance market would be ready to move some of its business to the EU as soon as Britain invoked Article 50 of the EU's Lisbon Treaty, which triggers the start of exit from the bloc.
Lloyd's chief executive Inga Beale said: "Clearly the UK's referendum on its EU membership is a major issue for us to deal with and we are now focusing our attention on having in place the plans to ensure Lloyd's continues trading across Europe."
KPMG said 72% of the CEOs surveyed had voted to remain in the EU.
The survey, which covered 100 UK CEOs with annual sales of at least £100mln and at least 500 staff, took place over four weeks from mid-July 2016 – one month after the UK voted to leave the EU.