The future relationship between Britain and the European Union will take years to negotiate and the UK can expect a hefty bill as the price of exit, European Commission president Jean-Claude Juncker has warned.
Mr Juncker said Britain must understand that it will not be able to negotiate a "cut-price or zero-cost" exit from the EU, but will have to settle the bill for commitments which it entered into as a member.
Discussions are underway in Brussels on the size of the bill to be presented to Prime Minister Theresa May when she launches withdrawal talks, with unconfirmed reports suggesting the demand may be as high as 60 billion euros (£51bn) over the next six years.
The sum will cover the UK's share of the cost of projects and programmes which it signed up to as part of the 28-nation bloc, as well as pensions for EU officials who served during its 45-year membership
Mr Juncker used a French slang term to tell the Belgian Federal Parliament in Brussels that he expected the bill to be very "salty" - meaning hefty or pricey.
"Our British friends need to know - and they know it already - that it will not be cut-price or zero-cost," said the Commission president. "The British will have to respect the commitments which they played a part in agreeing.
"Therefore the bill will be - to use a rather vulgar term - very salty. It will be necessary for the British to respect commitments which they freely entered into."
Mr Juncker stuck to Brussels' position that withdrawal arrangements - including the "exit bill" - must be agreed before moving on to potentially lengthy negotiations over future trade relations. The UK Government insists that these talks can run in parallel after Mrs May kicks off negotiations under Article 50 of the EU treaties - something she has promised to do by the end of March.
The Commission president told Belgian parliamentarians: "This will be a difficult negotiation, which will take two years to reach agreement on the exit arrangements.
"To agree on the future architecture of the relations between the UK and EU, it will need years."
He restated the Commission's position that there will be no membership of the European single market for the UK unless it signs up to freedom of movement for workers.
"Those who want to benefit from the advantages of the single market must respect the four fundamental freedoms, including the one which relates to the movement of workers," he said.
Mr Juncker described Brexit as "a crisis which concerns us all" and said that it made him personally "sad" to see a major European actor leave the EU.
"We need to settle our affairs not with our hearts full of a feeling of hostility, but with the knowledge that the continent owes a lot to the UK," he said. "Without Churchill, we would not be here - we mustn't forget that, but we mustn't be naive.
"Our British friends will need to understand that we want to continue to develop European integration."