Days before the Srebrenica massacre in July 1995, John Major was warned France had possibly brokered a secret deal with the Bosnian Serbs to halt airstrikes in return for the release of western military hostages.

This claim, detailed in a secret Foreign Office note to the prime minister, is among documents available to read at the National Archives in Kew fromTuesday that expose the depth of Anglo-French distrust during the Balkans conflict.

The papers reveal the newly elected French president, Jaques Chirac, was accused by British officials of “lunacy”, “grandstanding” and inconsistency over what should be done to protect vulnerable Muslim enclaves.

More than 8,000 men and boys were murdered in Srebrenica in early July 1995 after Bosnian Serb forces overran the town, which was designated as a safe area and protected by Dutch soldiers. The international criminal court for the former Yugoslavia later ruled the crimes amounted to genocide.

Key files and passages have been withheld from the release of government files under section 3 (4) the Public Records Act, but a picture nonetheless emerges of tension between Nato allies as they scrambled to respond to a succession of crises.

Facebook Twitter Pinterest Dutch UN peacekeepers watch Muslim refugees from Srebrenica, eastern Bosnia, gather in the nearby village of Potocari in July 1995. Photograph: AP

The Bosnian Serb seizure in May 1995 of more than 300 international peacekeepers, including 33 British soldiers in Goradze and Visograd, alarmed Downing Street.

Major spoke by phone on 28 May to the US president, Bill Clinton, who pledged that if hostages were harmed by the Serbs, “we gotta load up on them”. Parliament was recalled for an emergency sitting.

Sir Ivan Roberts, the British ambassador to Belgrade, met a contact on the Drina bridge at Zvornik and reported back that the Bosnian Serbs wanted assurances on Nato airstrikes before they released the hostages.

Plans were prepared for the UK’s 24 Air Mobile Brigade to be sent in as reinforcements. An inter-departmental row erupted over who should authorise deployment; on one letter, Major remarked: “A slippery note from MoD.”

In mid-June, however, the Bosnian Serbs began releasing hostages. On 28 June, Major assured parliament: ‘No deal was done … to secure the release … Nor has any undertaking been given by [Nato] member governments or commanders on the ground about future airstrikes [to deter Bosnian Serb attacks].”

The prime minister was cautioned in a secret note two days later by the MoD that he should not give such categoric assurances. “The position is that both the UN and the French government have publicly denied any deal over hostages,” recorded Sam Sharpe, the private secretary to the foreign secretary, Douglas Hurd.

But Gen de La Presle, acting on French instructions, had “visited Pale for contacts with Bosnian Serbs”. Swedish officials claimed “there were parallel telephone contacts between Chirac and Milosevic”.

Facebook Twitter Pinterest Serbia’s president, Slobodan Milošević, France’s president ,Jacques Chirac, and Bosnia’s president, Alija Izetbegović, in October 1996 during Bosnian peace talks. Photograph: Gerard Fouet/AFP/Getty Images

The note added: “We are unlikely to ever know the full truth about all of this … it is plausible that Chirac told Milosevic that airstrikes in the immediate aftermath of hostage releases were unlikely but stopped short of any formal undertaking …”

A covering note by Roderic Lyne, Major’s principal private secretary, informed the prime minister: “What this tells us speculatively is that the French may have done some sort of a deal but we don’t know for sure and they are denying it.” In turn, Major added a handwritten comment: “possible … but I doubt it was as firm as a deal”.

Days later, on 9 July, Alija Izetbegović, the Bosnian president, sent Major an urgent letter warning that “the Serb aggressor” has launched “a massive mechanized-infantry attack” on Srebrenica. UN peacekeeping troops, he warned, “are not willing nor capable of protecting the city under attack”.

He continued: “More than 60,000 civilians, predominantly women, children and the elderly, have found themselves in life threatening danger. I urge you to … prevent new acts of terrorism and genocide against the civilian population of Srebrenica.”

Two days later, Lyne reported there had been airstrikes that knocked out three tanks, but “a third close air support operation was about to be mounted when the Dutch UNPROFOR commander had it halted because the Serbs were threatening to kill [Dutch soldiers taken as hostages]”.

There was limited sympathy for the Bosnians. The MoD said there had been “little or no resistance by Bosnian govt forces”. When the Dutch “first took up their position forming a line against the Serb advance a couple of days ago, they took a number of shots in the rear from the Muslims”.

The overwhelming concern in Whitehall was whether British troops in another enclave, Goradze, would be targeted next and whether they should be reinforced or evacuated.

An air evacuation plan, codenamed Operation Screwdriver, was devised. Major was not impressed. “Not at all an easy option: cock up factor clearly present,” he commented in a handwritten annotation.

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On 15 July, Major spoke by phone to Clinton, admitting the situation “looked grim”. Clinton said: “Chirac was all over the place. Yesterday he seemed to be arguing for withdrawal. Today he wanted to reinforce Goradze and Sarajevo.”

Following a telephone discussion with a French official, Lyne informed Major: “Chirac felt there had to be some action we could take – between peace-keeping and war-fighting – to deter the Serbs. I explained some of the military problems of trying to be half-pregnant.

Lyne warned against precipitate military action but concluded: “This is no guarantee against further grandstanding or lunacy by Chirac.”

That same day, the first indication of the enormity of the tragedy in Srebrenica featured in a report from Lt Gen Rupert, in charge of UN forces in Bosnia. He informed London that the town was “empty of Muslims and already being occupied and looted by Serbs”. There were “unconfirmed reports of a massacre of a mixture of armed men and refugees”.