Britain must not be better off outside the European Union after Brexit, an eight-month inquiry by the French Senate has concluded.

The 51-page document also says Theresa May’s keynote Brexit speech at Lancaster House was a “mixture of veiled threats and pledges of goodwill” – a likely reference to the Prime Minister’s threat to take Britain out of the EU with no deal, rather than a bad deal.

The report adds that the EU’s four freedoms – goods, people, services and capital – are “inseparable” and it must not be possible for Britain to segment access to the tariff-free single market for certain sectors. “It is on this issue that the Senate will be very vigilant,” the report warns.

The report suggests that the divorce terms of Brexit have to be completed before negotiations over Britain’s future trading relationship with the EU commence. But the UK’s final agreement must not place it in a better position outside the EU, it adds.

Last week Jean-Pierre Raffarin, a former French premier who chaired the inquiry, said: “From a European point of view ... the new agreements cannot be better than the old ones – which might be difficult for the United Kingdom side to accept – while at the same time protecting the EU’s joint interests, notably on security and defence.”

The report says that Brexit is a shock to European cohesion but the process, which it claims is now “inevitable”, must not take the European project “hostage” and says unity of the 27 other EU states is a priority.

It comes after a senior German politician warned that Britain’s exit from the EU will be “mission impossible” and create “a lot of damage” for the UK. MEP Manfred Weber, leader of the European People’s Party, the largest political group in the European Parliament, said the process of Brexit would not be an easy task.

How Brexit affected Britain's favourite foods from Weetabix to Marmite Show all 8 1 /8 How Brexit affected Britain's favourite foods from Weetabix to Marmite How Brexit affected Britain's favourite foods from Weetabix to Marmite Weetabix Chief executive of Weetabix Giles Turrell has warned that the price of one of the nation’s favourite breakfast are likely to go up this year by low-single digits in percentage terms. Reuters How Brexit affected Britain's favourite foods from Weetabix to Marmite Nescafé The cost of a 100g jar of Nescafé Original at Sainsbury’s has gone up 40p from £2.75 to £3.15 – a 14 per cent rise—since the Brexit vote. PA How Brexit affected Britain's favourite foods from Weetabix to Marmite Freddo When contacted by The Independent this month, a Mondelez spokesperson declined to discuss specific brands but confirmed that there would be "selective" price increases across its range despite the American multi-national confectionery giant reporting profits of $548m (£450m) in its last three-month financial period. Mondelez, which bought Cadbury in 2010, said rising commodity costs combined with the slump in the value of the pound had made its products more expensive to make. Cadbury How Brexit affected Britain's favourite foods from Weetabix to Marmite Mr Kipling cakes Premier Foods, the maker of Mr Kipling and Bisto gravy, said that it was considering price rises on a case-by-case basis Reuters How Brexit affected Britain's favourite foods from Weetabix to Marmite Walkers Crisps Walkers, owned by US giant PepsiCo, said "the weakened value of the pound" is affecting the import cost of some of its materials. A Walkers spokesman told the Press Association that a 32g standard bag was set to increase from 50p to 55p, and the larger grab bag from 75p to 80p. Getty How Brexit affected Britain's favourite foods from Weetabix to Marmite Marmite Tesco removed Marmite and other Unilever household brand from its website last October, after the manufacturer tried to raise its prices by about 10 per cent owing to sterling’s slump. Tesco and Unilever resolved their argument, but the price of Marmite has increased in UK supermarkets with the grocer reporting a 250g jar of Marmite will now cost Morrisons’ customers £2.64 - an increase of 12.5 per cent. Rex How Brexit affected Britain's favourite foods from Weetabix to Marmite Toblerone Toblerone came under fire in November after it increased the space between the distinctive triangles of its bars. Mondelez International, the company which makes the product, said the change was made due to price rises in recent months. Pixabay How Brexit affected Britain's favourite foods from Weetabix to Marmite Maltesers Maltesers, billed as the “lighter way to enjoy chocolate”, have also shrunk in size. Mars, which owns the brand, has reduced its pouch weight by 15 per cent. Mars said rising costs mean it had to make the unenviable decision between increasing its prices or reducing the weight of its Malteser packs. iStockphoto

Speaking at a news conference in Strasbourg alongside the European Parliament’s chief Brexit negotiator, Guy Verhofstadt, the German MEP said: “When I have a look at the content and the topics on the table, for me it is still mission impossible ahead of us but we can manage this.”

Mr Weber added: “This will create a lot of damage, especially for the Brits, for sure, nobody had the wish to do this but it is the reality. We have to start to recognise this. This will not be an easy task ahead of us, especially having in mind to defend the interests of the European Union.

“It will be a mirror, from my point of view, to show the people in the European Union that it is much more better to reform the European Union than to destroy the European Union.

“It will show what Europe is all about.