The British government is refusing to release documents which could shed light on the fate of three Israeli soldiers missing since 1982 because it says sensitive information could harm diplomatic relations with Syria.

On June 11 1982, three Israeli soldiers went missing after a battle with Syrian and Palestinian forces near the Lebanese village of Sultan Yaqub in the last moments of the Lebanon war. Zachary Baumel, Yehuda Katz and Zvi Feldman, all in their 20s at the time, are still officially MIA - missing in action.

But Britain's ambassador to Syria, Ivor Lucas, filed a report to London on the day of the battle and may have witnessed the soldiers' capture by Syrian forces, who reportedly paraded them and their tank through Damascus.

Now a Manchester legal team, acting for Zachary Baumel's mother Miriam, is taking action under increased suspicion over silence from the UK government. Two years of failed requests by Mrs Baumel to see the Lucas report have resulted in the Foreign Office response: "We are conscious that the release of sensitive information would cause harm to our relationship with Syria."

In August the Manchester lawyers submitted a Freedom of Information Act appeal against the Foreign Office over its refusal to release Mr Lucas's report, which may be the only written record to shed light on the soldiers' fate. But two months after the appeal was launched, the FCO has stalled in setting a date to consider the matter.

Solicitor Daniel Berke believes the government can be forced to release the document on the grounds of public interest.

He said: "It is in the public interest to [show] that under its obligations under UK and international law, no passage of time will stop Britain aiding an ally, in this case Israel, to gain fair treatment for its soldiers and to counter terrorism. It is our view that the suggestion this 30-year-old document will cause some harm to Syrian-British relations is really quite a nonsense."

Ivor Lucas, now retired from the diplomatic service, refused a request by the JC to speak on the matter.

But Rev Bob Carroll, a British Christian minister and founder of MIA UK, dedicated to facilitating the release of Israel's service personnel, said he has met Mr Lucas and is sure he saw the fate of the soldiers.

An FCO spokesman would not comment on the appeal but said: "We stand ready to help the families involved as best we can. But the FCO continues to believe that the decision not to release the information best serves the public interest. We take our obligations under the Freedom of Information Act extremely seriously. "

Miriam Baumel said: "I just want the public to know this is a humanitarian matter. We keep getting information that these boys and my son were seen in Damascus and that there were witnesses, and anyone who saw something or who could help must help.

"I feel the possibilities are great that he is still alive, but certainly the families of those who were seen in Damascus are entitled to closure.

"I am calling on the British government to act in a humanitarian manner and let the families know by releasing this document, for us to go further in finding our children. If you have children, if one of your children would be lost, how would you feel?"