Rebel Tory MPs have launched an attempt to prevent the Government signing new trade deals after Brexit without Parliament's approval.

Fresh amendments tabled to a key Brexit bill would force ministers to give MPs and peers the power to amend or veto dozens of potential deals, amid fears ministers are planning to force them through without parliamentary scrutiny.

The MPs, who are also seeking to force the Government to keep the UK in a customs union with the EU, believe they are likely to secure the support needed to pass the amendments, if opposition parties back them.

Government ministers have said they want to “roll over” roughly 100 trade deals the EU has with around 60 countries into bilateral agreements between the UK and those countries after Brexit. They insist these would be on existing terms and so would not require fresh parliamentary approval.

However, MPs fear countries are unlikely to give the UK alone the same terms as the EU’s 27 other members and their combined 500 million inhabitants. That means UK ministers would have to negotiate a deal under new conditions – something they would currently be able to do without Parliament’s approval.

This has triggered concerns that existing standards could be lowered or conditions attached that would force the UK to offer concessions, such as granting a certain number ofvisas each year to a country’s citizens.

Countries such as Australia and New Zealand have already indicated they would want visa guarantees to be part of a future trade agreement with the UK. Other nations, including those that already have deals with the EU, are expected to follow suit.

The new amendments were tabled by Tory MP Jonathan Djanogly and signed by five other Conservatives, including several former ministers.

Dominic Grieve, Anna Soubry, Antoinette Sandbach, Robert Neill and Stephen Hammond have all pledged their support and more Conservatives are expected to follow suit.

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Mr Djanogly told The Independent: “As things stand, a new trade agreement would be negotiated by the EU. This would involve the terms going through a rigorous and lengthy regime of scrutiny both in Brussels and the UK Parliament, usually ending with a vote of each member state.

“However, under the Trade Bill post Brexit, the Government is asking for powers to roll-over existing EU trade bills with little or no scrutiny. My amendments essentially provide that where the rolled-over free trade agreement actually has changes from the original, then there should be parliamentary scrutiny.”

“If, for example, one of the sixty countries agreed to roll-over their existing EU agreement to the UK, but only if the UK introduced a liberal new visa regime, then I would have thought that such a varied agreement would be of general concern to Parliament and ought to be subject to scrutiny.”

The new amendments were tabled to the Trade Bill yesterday and pile fresh pressure on Downing Street over a piece of legislation that is already proving to be a major headache.

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A cross-party amendment to the same bill would force ministers to keep the UK in a customs union with the EU. It is thought to have enough support among Tory backbenchers to be passed, if Labour agrees to back it.

A third set of proposed changes, due to be tabled by Stephen Hammond, will seek to force the Government to sign the UK up to the European Free Trade Association (EFTA).

The Government is likely to delay debate on the bill until after local elections in May in an attempt to allow time to reach an agreement with Conservative backbenchers.

Mr Djanogly’s proposed changes would give ministers the right to sign new deals with countries on exactly the same terms as the EU’s existing agreements, but force them to seek parliamentary approval if the conditions change in any way.

The bill in its current form would allow the Government to sign new deals, including on different terms, without MPs or peers being given a say.

A Department for International Trade spokesperson said: “The Trade Bill respects the principle of parliamentary sovereignty. It is about maintaining the effects of our current trading arrangements, to secure continuity for businesses and consumers as we leave the EU.

“It is clearly in the interest of our country and our trading partners that these arrangements – that will have already been scrutinised at an EU level and overseen in the UK by Parliament’s EU Select Committees – are transitioned quickly and smoothly.