The government has spent £97 million on consultants whilst preparing for Brexit, a watchdog has said.
Cabinet Office figures showed £65 million was spent on consultants in the year to April 2019 - but the National Audit Office (NAO) estimated the total costs from Brexit-related consultancy to be 50 per cent higher after a review.
The NAO investigation uncovered an additional £32 million in Brexit consultancy expenditure by government departments to April this year, including costs from the EU referendum until April 2018.
Auditor general Sir Amyas Morse's report sets out how there was "little oversight" of departments' expenditure on Brexit-related consultancy before April 2018.
But Sir Amyas added that the Brexit preparations had been a "significant challenge" for the government.
The NAO said government departments were failing to meet transparency standards, including publishing details of contracts awarded within 90 calendar days.
While other consultancy contracts took an average of 82 days to be published, the average for Brexit consultancy contracts was 119 days and all that had been published were "significantly redacted".
Labour MP Meg Hillier, Westminster's Public Accounts Committee chairwoman, said it was "not good enough" that the Cabinet Office, which is responsible for improving government efficiency, appeared to have lost track of 50 per cent of the consultancy costs.
She added: "The Cabinet Office must ensure that departments' use of consultants, and the money spent, is fully open to public scrutiny."
A Management Consultancies Association spokeswoman said consultants had been "proud to provide expert support" and "provide value for money".
She said: "Departments have faced an unprecedented volume of workload planning for all Brexit scenarios and using external resources has enabled the government to work quickly and with intensity on major programmes across the UK.”
A government spokesman defended the spending, which he said was "cost-efficient".
He said: "It is often more cost-efficient to draw upon the advice of external specialists for short-term projects requiring specialist skills.
"These include EU exit priorities such as ensuring the uninterrupted supply of medical products and food to the UK."