Parliament will have the power to “delay exit from the EU indefinitely” unless the “meaningful vote” defeat in the House of Lords is overturned, Liam Fox says.

The International Trade Secretary condemned peers for defying the referendum result, in inflicting the defeat on Theresa May – but also admitted it had given MPs the chance to exert a huge amount of influence over the exit process.

“The implication of the Lords amendment last night is that we could be delaying exit from the EU indefinitely,” Dr Fox protested.

“It is a backdoor mechanism, in my view, for trying to block the democratic will.”

However, he stopped short of vowing to reverse the vote in the Commons, where pro-EU Tories are increasingly confident they can overturn the upper house's amendment.

The comments come after peers voted to ensure parliament – rather than the government – decides the next steps if the prime minister’s exit deal is rejected in the autumn.

Unless the defeat is overturned by MPs, it increases the chances of sending the government back to the negotiating table, or even forcing a fresh referendum on Brexit.

Brexit threatens life on the Irish border: in pictures Show all 15 1 /15 Brexit threatens life on the Irish border: in pictures Brexit threatens life on the Irish border: in pictures An abandoned shop is seen in Mullan, Co Monaghan. The building was home to four families who left during the Troubles. The town was largely abandoned after the hard border was put in place during the conflict. Mullan has seen some regeneration in recent years, but faces an uncertain future with Brexit on the horizon Reuters Brexit threatens life on the Irish border: in pictures A defaced ‘Welcome to Northern Ireland’ sign stands on the border in Middletown, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Mervyn Johnson owns a garage in the border town of Pettigo, which straddles the counties of Donegal and Fermanagh. ‘I’ve been here since 1956, it was a bit of a problem for a few years. My premises has been blown up about six or seven times, we just kept building and starting again,’ Johnson said laughing. ‘We just got used to it [the hard border] really but now that it’s gone, we wouldn't like it back again’ Reuters Brexit threatens life on the Irish border: in pictures Farmer Gordon Crockett’s Coshquin farm straddles both Derry/Londonderry in the North and Donegal in the Republic. ‘At the minute there is no real problem, you can cross the border as free as you want. We could cross it six or eight times a day,’ said Crockett. ‘If there was any sort of obstruction it would slow down our work every day’ Reuters Brexit threatens life on the Irish border: in pictures John Murphy flies the European flag outside his home near the border village of Forkhill, Co Armagh Reuters Brexit threatens life on the Irish border: in pictures Potter Brenda McGinn stands outside her Mullan, Co Monaghan, studio – the former Jas Boylan shoe factory which was the main employer in the area until it shut down due to the Troubles. ‘When I came back, this would have been somewhere you would have driven through and have been quite sad. It was a decrepit looking village,’ said McGinn, whose Busy Bee Ceramics is one of a handful of enterprises restoring life to the community. ‘Now this is a revitalised, old hidden village’ Reuters Brexit threatens life on the Irish border: in pictures Union Flag colours painted on kerbstones and bus-stops along the border village of Newbuildings, Co Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures Grass reflected in Lattone Lough, which is split by the border between Cavan and Fermanagh, seen from near Ballinacor, Northern Ireland Reuters Brexit threatens life on the Irish border: in pictures Donegalman David McClintock sits in the Border Cafe in the village of Muff, which straddles Donegal and Derry/Londonderry Reuters Brexit threatens life on the Irish border: in pictures An old Irish phone box stands alongside a bus stop in the border town of Glaslough, Co Monaghan Reuters Brexit threatens life on the Irish border: in pictures Billboards are viewed from inside a disused customs hut in Carrickcarnon, Co Down, on the border with Co Louth in the Republic Reuters Brexit threatens life on the Irish border: in pictures Seamus McQuaid takes packages that locals on the Irish side of the border have delivered to his business, McQuaid Auto-Parts, to save money on postal fees, near the Co Fermanagh village of Newtownbutler. ‘I live in the south but the business is in the North,’ said McQaid. "I wholesale into the Republic of Ireland so if there’s duty, I’ll have to set up a company 200 yards up the road to sell to my customers. I’ll have to bring the same product in through Dublin instead of Belfast’ Reuters Brexit threatens life on the Irish border: in pictures A disused Great Northern Railway line and station that was for customs and excise on the border town of Glenfarne, Co Leitrim Reuters Brexit threatens life on the Irish border: in pictures Alice Mullen, from Monaghan in the Republic of Ireland, does her shopping at a former customs post on the border in Middletown, Co Armagh. ‘I’d be very worried if it was a hard border, I remember when people were divided. I would be very afraid of the threat to the peace process, it was a dreadful time to live through. Even to go to mass on a Sunday, you’d have to go through checkpoints. It is terribly stressful,’ said Mullen. ‘All those barricades and boundaries were pulled down. I see it as a huge big exercise of trust and I do believe everyone breathed a sigh of relief’ Reuters Brexit threatens life on the Irish border: in pictures A bus stop and red post box stand in the border town of Jonesborough, Co Armagh Reuters

Dr Fox warned of a public backlash if peers continued to throw up obstacles, but tried to scotch talk that a further referendum may be the only way out of any impasse.

“Even the House of Lords, last night, rejected having another referendum. I think that when we have taken a decision, we follow it through,” he said.

Dr Fox insisted crashing out of the EU with no agreement – a threat repeatedly made by the prime minister – was still on the table, but downgraded it to a “possibility”.

He also tried to rule out compromise on the policy of staying out of a customs union with the EU, saying: “We would be in a worse position than we are today.

“We would have to accept what the EU negotiated in terms of market access to the UK, without the UK having a voice.”

He added: “A customs union is what Turkey has – it would still leave us accepting rules made by Brussels with no say in how they are made.”

Dr Fox hinted strongly that he would resign if the prime minister does give way, refusing to answer the question directly, but adding: “Getting no answer you can draw your own inferences.”

When, on BBC Radio 4’s Today programme, it was put to him that Ms May was a “horribly weakened” prime minister, he replied: “We don't have a parliamentary majority, that's for sure. That makes life harder.”

The interview came one day before a potentially decisive meeting of the Brexit sub-committee, which will see an attempt by Brexiteers to kill off Ms May’s preferred plan for post-Brexit customs.

They fear the “partnership” plan – which would see the UK collecting tariffs on the EU’s behalf – is unworkable and could be used by Brussels as a device to soften Brexit.

The alternative “maximum facilitation” option is based on technological solutions to the customs issue but the EU is sceptical that it would ever work.