Ministers have been urged to spell out how much it will cost Britain to replace European Union regulatory agencies after Brexit.
The Liberal Democrats called for clarity from the Government amid reports that the UK could still fall under the remit of certain EU agencies after leaving.
According to the Financial Times, officials are preparing for the UK to remain under the regulation of some agencies because the country does not have the time or expertise to get new ones ready in time for the UK's scheduled departure in 2019.
Prime Minister Theresa May is due to trigger the two-year exit process under Article 50 of the EU treaties on Wednesday.
Lib Dem foreign affairs spokesman Tom Brake said: "Theresa May's claim the UK can leave the EU without a deal in place has been left in tatters.
"It's now obvious that crashing out without a deal would be a bureaucratic nightmare, inflicting huge damage to our economy and costing the taxpayer millions.
"The Government must clarify which EU agencies it plans to replace and at what cost to the public purse.
"At the end of this process, the British people must be given the final say on the Conservative Brexit deal."
A Department for Exiting the European Union spokesman said: "The UK is leaving the EU and will be ready for all outcomes of negotiations.
"There are a number of EU agencies which enforce particular regulatory regimes, or facilitate information sharing.
"As part of exit negotiations, the Government will discuss with the EU and member states the UK's future status and arrangements with regard to these agencies, and will consider all practical options."