The government has quietly ruled out compensating black African veterans of the second world war who were paid a third as much as their white counterparts.

Following months of silence since the Guardian and al-Jazeera first revealed the discriminatory policy, the defence minister Tobias Ellwood has privately told MPs there were “no current plans to take forward any further investigations of this matter”.

Officials across three government ministries examined the issue after revelations that soldiers drawn from Britain’s African colonies were paid an end-of-war bonus that was calibrated not only to rank and length of service but also ethnicity. White soldiers from those colonies received a gratuity worth triple that offered to black troops.

In a letter seen by the Guardian, Ellwood said a full investigation would require “extensive resources”. He cited “competing demands” across government departments and the “difficulty in establishing an accurate factual records base”.

Ellwood added that the decision “in no way diminishes how grateful the UK is to all those servicemen and women from the Commonwealth who served with Britain during the second world war.”

In the letter, the minister acknowledged that non-white troops had faced discrimination in Britain’s armed forces. “As we look back in time, we often encounter disparities that would never be acceptable by today’s standards.”

His letter was in response to a written question from Richard Benyon, a Conservative MP and former lieutenant with the Royal Green Jackets, an infantry regiment in which Ellwood also served.

Labour strongly condemned the decision to shelve further inquiries. “It beggars belief that the government simply cannot be bothered to investigate how many black African veterans who faced this appalling discrimination are still alive, and compensate them while there is still time to do so,” said Emily Thornberry, the shadow foreign secretary. “We need to hear from Boris Johnson and Jeremy Hunt as to whether they will reverse this shameful inaction.”

Fabian Hamilton, the shadow minister for defence and foreign and Commonwealth affairs, demanded “a proper apology without delay”. He said: “This was systematic and deliberate discrimination, and an unacceptable way to treat those who were an integral part of the war effort that kept our democracy safe from fascism and Nazism. This government’s treatment of these veterans is a disgrace.”

Conservative backbenchers have also called for action. Tom Tugendhat, the chair of the foreign affairs select committee, who previously served as a lieutenant colonel in Iraq and Afghanistan, said: “The difference in pay between heroes who fought side by side in our common struggle against tyranny is clearly wrong … The government should apologise.”

Andrew Mitchell, a former cabinet minister, said: “There will not be many elderly African soldiers who served the crown at that time still alive. But those who are should be compensated and given an apology.”

Richard Benyon, who sits on the intelligence and security committee of parliament, urged the government to “recognise that discrimination on the grounds of ethnicity when [the wartime] experience was exactly the same was totally wrong”. He added: “Given that it is a very small number of people left alive, some recognition of that wrong – both verbal and financial – should be made.”

During the war Britain recruited – in some cases forcibly – more than 600,000 African men from across the continent. They fought in some of the war’s bloodiest campaigns, including Burma where they clashed with Japanese imperial forces in dense jungle and torrential rain, sustaining significant casualties.

Among the survivors was Muchara Ntiba, a Kenyan veteran now aged 97. Remembering fierce combat in the far east, he said: “Burma was tough. Bullets were just raining on us.”

He described corporal punishment at the hands of superiors, despite the British army officially having outlawed the practice decades earlier. “We would give them the palms of our hands to be beaten,” he said. “Afterwards, even an attempt to hold something would be hard.”

Ntiba, who still suffers with back pain from a wartime injury, is among the last surviving African veterans of his generation. “We put our lives in danger for them,” he said. “The British government did not listen to our demands. We got out with nothing.”

The Ministry of Defence said the UK “remains indebted” to African servicemen and women, but said that the soldiers involved were employed by their respective governments, not the UK Army, making it difficult to establish the full facts.