Juan Manuel Santos says he wants consensus for a deal with the Farc – but is not prepared to risk further delay

The president of Colombia – and this year’s Nobel peace laureate – Juan Manuel Santos has pledged to deliver a peace accord by Christmas to end the world’s longest-running war.

President Santos was unexpectedly awarded the Nobel prize this month just days after a peace deal that his government forged with the Marxist guerrilla movement, the Fuerzas Armadas Revolucionarias de Colombia (Farc), had been narrowly defeated in a plebiscite. The rejected peace accord would have seen the Farc lay down its arms and become a political party, in addition to introducing land reforms and compensation for victims of the 50-year war.

However, critics attacked one of the central tenets of the deal – the so-called system of “transitional justice”, which meant Farc leaders could have avoided lengthy jail terms in return for confessing their crimes and working to build peace –saying it was too lenient.

In an interview with the Observer on the eve of the first state visit by a Colombian president to the UK, Santos makes his most robust commitment yet to finding a new peace accord since losing the plebiscite. He said he hoped an amended accord would not only be agreed with the Farc but also ratified – either by congress, another plebiscite or through other means – by Christmas.

Preparing for peace: inside Farc’s Colombian jungle base Read more

He added that he was willing to proceed, if necessary, without input from the leader of the No vote, his political nemesis, the influential former president, Álvaro Uribe. “I hope that Uribe will also come on board because we want as large a consensus as possible,” said the president. But he continued: “If [Uribe] decides not to join the bandwagon, then he will simply be isolated and we will continue with the other people [who previously opposed the accord] because we cannot simply stop the process – because it will come to an end if we do not continue it.”

Facebook Twitter Pinterest Alvaro Uribe, who led the No campaign, with his supporters after voters rejected the peace deal earlier this month. Photograph: STR/AFP/Getty Images

Colombians had been expected to vote Yes to the peace accord and its rejection was a huge setback for the president whose team have been negotiating the peace accord over the past four years in Havana, Cuba. Santos says now that since the result “we started a national dialogue with all the promoters of the No vote to see what changes they would like in the agreement, because they all said that they wanted peace”.

He said that “all the negotiators and I have met almost every organisation and we are now digesting more than 500 proposals – and talking with the Farc – to have a new agreement, agreed and approved, by Christmas. That is my goal.”

He warned that further delay could imperil the process. “This uncertainty is very risky, because anything could happen that could really make the process explode. So I am working 24 hours a day, seven days a week, with my team to get another agreement.”

Asked what mechanism would be used to legitimise the new agreement, Santos said he had a range of options under consideration, but that the priority now “was to get a new deal as soon as possible”.

He said: “Whatever mechanism I use to implement it, whether through congress, or through municipal councils or through another plebiscite or a combination, I will decide as soon as we have a new agreement and see what would give it the best legitimacy, both politically and legally.”

Colombia’s war began in 1964, with the foundation of the Farc by communist peasants defending the autonomous communities they had declared in protest against unequal land ownership. The war – which became entwined with those waged by drug cartels and rightwing paramilitaries – has cost more than 200,000 lives, according to most estimates, and displaced almost six million people.

Santos and his peace accord have come under sustained criticism from Uribe, who said in Miami last week that the deal would lead to “a second Venezuela” in Latin America – suggesting that the Farc’s entry into politics would reduce the country to the status of their flagging socialist neighbour.

We are pushing very hard to have meetings with Uribe's team. Some meetings have taken place President Santos

In the interview, Santos responded to suggestions that he had not reached out sufficiently to Uribe since the plebiscite: “We are pushing very hard to have meetings with [Uribe’s team]. Some meetings have taken place, today, just an hour ago … through the radio Uribe had asked for a meeting with me, I said ‘of course I would meet him’ … I would meet him any time. He then said ‘no’ and that it is better that the teams get together. And I said ‘of course, my teams are ready’, not just now but have been ready for the last three weeks and he has been stalling, not allowing the teams to get into real negotiations. I am ready, I am eager, because I know that if we sit down we can agree on many of the things that concern him.”

Having lost the plebiscite by only 0.4% of the vote, Santos aims to incorporate changes suggested by the No camp in an effort to get the deal through.

And yet, he insisted that there were some proposals from the No campaign that would not be considered in any new peace accord. “Some of the proposals are viable and we think the Farc should accept them, but others are simply not viable: for example the ones that say there is no armed conflict in Colombia, and that there is no war in Colombia and that there are no victims in Colombia and therefore the transitional justice cannot apply.

“That type of proposal is simply not viable, and so we are discarding those radical positions and concentrating on what is practical, what is really an improvement on the current peace accord, taking into account the No vote, not only Uribe, but also many of the other No promoters.”

President Santos singled out the religious constituency which supported the No campaign as one he may have won round to a new accord. “Probably the largest number of people who voted against the agreement did not do so because of the peace agreement but because the churches – the Catholic church and the [evangelical] Christian church – said that the agreement was defending what they called a ‘gender ideology’ which is absolutely not true. We have changed the wording and I think they now are absolutely for the agreement. Those type of changes we are making every day and we hope to have the new agreement ASAP.”

Facebook Twitter Pinterest Farc guerrillas preparing to return to civilian life before the peace process was interrupted by the plebiscite. The ceasefire has been extended. Photograph: Stephen Ferry/The Guardian

Santos’s state visit to the UK will include a banquet hosted by the Queen on Tuesday night and meetings with Theresa May at Downing Street and – perhaps most poignantly – a visit to Northern Ireland, where his diplomats have been busily engaged in consultations over the peace the British government forged there in 1998.

He said the UK has been “a tremendous support in this process”, including at the UN security council, where “they were the pen holders” over “a mandate to the secretary general to participate in the monitoring of the ceasefire. The UK has always supported the peace process, so I only have words of gratitude for the British in helping Colombia to achieve peace after 50 years of war.”

May told the Observer: “We will continue to support the president as he works to secure a final and lasting agreement, including through our leadership at the UN security council. We are sharing practical advice based on our experience in Northern Ireland, which taught us that peace-building takes time, perseverance and patience.”

On Wednesday, the prime minister will welcome Santos to Downing Street, where they will have a bilateral meeting and are expected to discuss a range of issues. In a post-Brexit environment, trade and business will doubtless figure. As May says, “the UK has been Colombia’s third largest foreign investor over the past decade, and our trading relationship was worth £1 billion last year”.

It will be the only state visit the UK is hosting this year, and May’s first.

Santos will spend a day in Belfast, where he will visit a reconciliation centre and learn about the measures taken by the two communities in Northern Ireland to solidify the peace process since the signing of the 1998 Good Friday Agreement.

Asked whether the urge towards a reworked accord was connected to his return to Europe in mid-December to collect the Nobel prize in Oslo, Santos said: “The Nobel comes at the most opportune time. It has helped a lot to push forward this new agreement. I am not doing it because of that, but because of the urgency ... it has to be in the next days or next couple of weeks.”

•An earlier version of this story used the phrase ‘ideology agenda’ instead of ‘gender ideology’ due to a translation error. This version has been corrected