Thomas Watters: Last known survivor of the Scots volunteers in the Spanish Civil War

Watters, far right, with his ambulance unit in Glasgow in 1937 before departing for his second stint in Spain (Getty Images)

Thomas Watters, who has died aged 99, was the last known survivor of the 550 volunteers from Scotland who served in the Spanish Civil War of 1936-39.

Most were Communists and socialists and enlisted in the International Brigades to fight for the Spanish Republic against General Franco's fascist-backed rebel army. But Watters always declared himself to be apolitical and said that it was humanitarian rather than political motives that took him to Spain as a member of the independent Scottish Ambulance Unit.

Watters had been studying first aid with the Red Cross for several years while working as a Glasgow bus driver, having trained as a motor mechanic after leaving school in Tillicoultry. So when he heard the appeal for Scottish drivers and medics to go to Spain he felt he was well qualified for the challenge. Glasgow Corporation helped by agreeing to keep his job open.

Following a financial appeal in which trade union members in Glasgow organised flag days and the local musicians' union staged a benefit concert, a large crowd saw six ambulances crewed by Watters and 18 other uniformed volunteers leave the city centre on 17 September 1936. It was barely two months since Franco had launched his initially unsuccessful coup against the Spanish Republic with military backing from Hitler and Mussolini. Watters was to serve in Spain for most of the next two years.

He was immediately pitched into action in October 1936, helping the wounded as Republican militias and civilians retreated north in the face of the well armed and organised fascist advance south of Madrid. However, the Scottish Ambulance Unit was almost as quickly plunged into controversy. Even before leaving Scotland there had been charges of pro-Republican partisanship from right-wing sympathisers of General Franco. But in Spain, there were suspicions that members of the unit were helping Franco's rebels, in particular by smuggling fascist sympathisers out of the capital.

Claims also emerged that some had been involved in looting. Five volunteers were placed under house arrest in Madrid before deportation and another two were sent home for health reasons. Depleted though still determined, the remaining members, including Watters, returned to Scotland in December and launched another round of fund-raising activities.

By now the Foreign Secretary, Sir Anthony Eden, had praised the work of the Scottish Ambulance Unit and the new appeal attracted support from across the political and social spectrum in Glasgow. Backers included the Lord Provost, Sir John Stewart, and Sir Daniel Stevenson, the local philanthropist, businessman and chancellor of Glasgow University who had been the driving force behind the creation of the unit.

Watters, plus two of his original colleagues and seven new volunteers, was soon travelling south in two ambulances, leaving Dover on 19 January 1937 for the journey back to the Spanish capital. With the city effectively under siege by the Francoists and facing daily bombardments, they braved bombs and shells to organise civilian evacuations and to bring in emergency food supplies, with the unit winning praise from the Republican authorities for its "valuable solidarity".

Watters later recalled: "You never knew what was going to happen. People often asked, were you deliberately bombed or shot at? But if you go into the target area, whatever the target is, you've to take what comes, just the same as the fighting men. I had quite a few narrow shaves, mind you. But we fortunate enough to make it – plenty others didn't, unfortunately."

Controversy struck a second time when four members of the unit resigned in March and joined the International Brigades' Spanish Medical Aid Committee. Contrary to the officially neutral stance, they argued that the unit should remain behind Republican lines should Madrid fall to the fascists, as then seemed likely.

Again depleted, the unit travelled back to Scotland in July 1937, only to return to Spain in September. Watters was once more part of the team. With only one subsequent two-week break in Britain in February 1938, he continued his welfare and medical work until the unit was finally repatriated in July 1938. A few weeks later, on 9 August, he was awarded the Medal of the Order of the British Empire – better known as the British Empire Medal – for his efforts in Spain by Glasgow's Lord Provost.

During the Second World War Watters moved to St Albans to work as an engineer in the de Havilland aircraft factory in Hatfield. He stayed on there until his retirement, while the company name changed first to Hawker Siddeley and then British Aerospace. His wife Constance, "Connie", whom he met during the war in Spain while she was working as a translator, died in 1990 at the age of 89.

In his final years, Watters became active in the International Brigade Memorial Trust. He received Spanish citizenship at a ceremony at the Spanish embassy in London on 9 June 2009, along with eight International Brigade veterans. In August 2010 he spoke at the rededication of the memorial in Glasgow by the sculptor Arthur Dooley to the Scottish volunteers in the Spanish Civil War; and in July last year, the 75th anniversary of the outbreak of the Spanish Civil War, he laid the wreath on behalf of the trust at the national memorial to the International Brigades on London's South Bank.

Speaking about his time in Spain, he said: "It was very hard. The language was a big problem and the weather was sometimes appalling. You think of sunny Spain but it could be very cold and miserable in the winter-time and some suffered. It was not just the fighting men; you had all the civilians as well, in Madrid especially. They suffered terribly as well."

Thomas Watters, Spanish Civil War volunteer: born Alloa, Clackmannanshire 16 February 1913; married 1939 (died 1990); died Welwyn Garden City 25 February 2012.