This is equivalent to a free cash injection worth 5 per cent of the total income of the firms analysed.
Typically, excess working capital is tied up with inefficient financial and operational processes.
Paul Trickett, corporate finance partner in Yorkshire, said: “The effective management of working capital can easily be overlooked, especially when the focus is on generating new growth.
“Yet this is a good time to focus on managing basic processes, as it could free up cash for investment.
“Last year’s increase is due in part to a shortening of supplier payment periods, as well as being a byproduct of growth.”
Deloitte’s report looked at the performance of UK listed companies with turnover greater than £60m.
The report found unlocking this excess working capital would be the cheapest source of finance to protect or grow shareholder value, rather than a bank loan or equity bonds.
Companies in the UK are becoming less efficient in the cash conversion cycle, said Deloitte.