LONDON (Reuters) - Lawyers for former Pakistan president Pervez Musharraf on Friday appealed to the United Nations to intervene and help prevent him being tried for treason, saying he faced a “show trial”.

Pakistan's former President and head of the All Pakistan Muslim League (APML) political party Pervez Musharraf salutes as he arrives to unveil his party manifesto for the forthcoming general election at his residence in Islamabad April 15, 2013. REUTERS/Mian Khursheed

Musharraf’s case, initiated by the Pakistani government, focuses on accusations that the former military leader breached the constitution when he imposed emergency rule in 2007.

The charges mark a serious challenge to the country’s powerful army and could result in the execution of a man who was once the most powerful in the country.

Musharraf’s trial is due to begin on December 24.

His plea, issued from London by an international legal team, is designed to get the United Nations to urge Nawaz Sharif, Pakistan’s prime minister, to delay or stop it.

It was sent to a U.N. special rapporteur who investigates complaints about the independence of judges and another who deals with cases involving the death penalty.

The rapporteurs have recently reported on high-profile cases in Sri Lanka and Iraq. The document was also sent to the U.N. High Commissioner for Human Rights.

His lawyers made the same appeal to the British, American and Saudi governments, citing what they said was Musharraf’s “immense assistance” to the West during his time in office.

Musharraf was a key ally of the United States in the aftermath of the September 11, 2001 attacks on New York and Washington, and U.S. aid to Pakistan, much of it in the form of military assistance, soared.

Musharraf’s lawyers said they had compiled a report for the United Nations supporting his case, saying the charges against him were revenge for his ousting of Sharif, the elected prime minister, in a 1999 coup when he was head of the army.

The judges in charge of the case had been selected by Sharif and would not conduct a fair trial, they said.

“Politicians have no business hand-picking judges to try their opponents,” said Steven Kay, a member of Musharraf’s legal team.

Nor, the lawyers’ report said separately, could the judges be regarded as impartial since they had been affected by a crackdown on Pakistan’s judiciary during Musharraf’s near-decade of military rule.

“The three judges appointed to try Musharraf’s case have such an obvious conflict of interest that it is reasonable to call them to withdraw,” the report said.

Civilian rule in Pakistan was restored in 2008, but the South Asian, nuclear-armed country has been governed by the army for more than half of its 66-year history since independence, and the military remains a potent political force.

Musharraf returned to Pakistan in March after nearly four years of self-imposed exile to contest a May 11 general election, but was disqualified from standing because of pending court cases.