Lesser was one of the last surviving British veterans of the Spanish Civil War, and went on to serve as chair of the International Brigade Memorial Trust (IBMT), and write for the Daily Worker and its successor, the Morning Star.

[13] He also later said that his training in the OTC, which was conducted in rural environments based on the experiences of the British Army in the First World War, was of little use in Spain where the fighting took place in cities.

[17] The CPGB gave Lesser money for a ticket to Paris and an address to report to when he arrived; from the Paris-Gare de Lyon he travelled by train to Perpignan.

[18] He took the pseudonym "Raimundo Casado" while crossing the Pyrenees,[5][10] and travelled to Figueres, then Barcelona,[19] then to the headquarters of the International Brigades in Albacete, where he trained.

[24] They were sent across Spain to Andújar[25] then went south to Lopera,[6][26] where in January 1937 (having previously suffered a shrapnel-inflicted head wound)[4] Lesser was hit by bullets in the back and foot, likely to have come from his own machine gun company.

[6][7][26] As his comrades had been forced to withdraw, Lesser remained in place until his friend Cunningham, who had insisted on looking for him, found him and, unable to locate a stretcher, dragged him away from the fighting.

[26] While recovering, he learned Spanish, was introduced to Miguel de Cervantes' Don Quixote,[5] and worked in the office of the newly-formed British Battalion in Albacete during the Battle of Jarama.

Crick speculated that the claims attributed to Frankford, in particular the admission that he had "committed the crime of taking part in the armed rising of Fascists against the anti-Fascist Government", may have been the inspiration for the "bizarre and pathetic" confessions made by characters in George Orwell's Animal Farm.

[35] Lesser then became a correspondent for the Daily Worker in Barcelona, using "Sam Russell" as his byline[6] and covering the Republicans' retreat at the border town of Figueres.

[4][6] He rejoined the newspaper in the final months of the war[7] and in 1945, following the lifting of the government's ban on publication of the Daily Worker, he flew in a Royal Air Force Avro Lancaster bomber dropping food supplies in the Netherlands.

[1][4] Writing for the Daily Worker, Lesser visited Jersey following its occupation, covered the 1952 show trial of Communist Party of Czechoslovakia general secretary Rudolf Slánský, and witnessed Nikita Khrushchev's rise to power.

[6] As foreign editor, Lesser was based in London but reported from Nigeria, where he covered the 1960 independence celebrations,[6] and from Cuba during the 1962 Cuban Missile Crisis, where he conducted a five-hour-long interview with Che Guevara.

Guevara told him that if the missiles had been under Cuban control, Cuba would have retaliated against perceived aggression from the United States by firing on American boats and cities.

[4] She lived with Lesser in Moscow during his time as a correspondent there, and on their return to England resumed nursing and was active in the Campaign for Nuclear Disarmament.

Lesser, in his capacity as the National Union of Journalists' Father of the Chapel, joined the Eurocommunist wing in opposition to Morning Star editor Tony Chater.

"[46] He also spoke of his sadness that so few of his comrades were still alive to witness the gesture, and quoted Laurence Binyon's "Ode of Remembrance":[45] Age shall not weary them, nor the years condemn.

In his book Unlikely Warriors, historian Richard Baxell wrote that Lesser "spoke clearly and eloquently ... though an occasional catch in his voice betrayed the emotional intensity of the occasion.

"[45] Tribune's obituary remarked that the speech showed "He may have moved away from communism to become an admirer of Tony Blair, but this was the old Sam Lesser fire.

"[3] In July 2009 he appeared at the International Brigade memorial in Lambeth's Jubilee Gardens, where he paid tribute to Jones,[47] and on 7 May 2010 he appeared at the unveiling of a plaque honouring the 90 members of the International Brigades killed at the Battle of the Ebro, where he gave a speech in Spanish condemning the lack of support shown to Republican volunteers by representatives of the British government.

[48] In his final weeks Lesser opened an exhibition about the International Brigades at the Marx Memorial Library and chaired an IBMT committee meeting in London.

[49] Lesser died in London on 2 October 2010 at the age of 95,[50] leaving instructions for his ashes to be scattered near the International Brigade memorial at Montjuïc in Barcelona.