Several conservative MPs on Sunday slammed British ambassador Simon Gass for criticising Iran's human rights record on his embassy website and calling for the release of a prominent lawyer.
"Simon Gass must learn the ethics of an ambassador," said Alaeddin Borujerdi, the head of parliament's foreign policy commission, quoted by the official IRNA news agency.
"It seems that Simon Gass in on a mission in Tehran to demolish relations between the two countries rather than establishing them," he said, as British and US flags were burnt during a demonstration outside the embassy.
Another senior MP, Heshmatollah Falahatpisheh, accused Gass of interfering in Iran's internal affairs and urged the foreign ministry to "seriously consider expelling the British ambassador," Fars news agency reported.
And MP Kazem Jalali said the parliamentary foreign policy commission would next week examine a downgrading of ties with Britain.
"It seems necessary to downgrade ties given the ambassador's frequent insolence ... and this is the least that Britain should pay," the deputy told Fars.
In remarks posted on the British embassy's website for Thursday's International Human Rights Day, Gass said that lawyers, journalists and NGO workers are "nowhere under greater threat than in Iran."
"Since last year human rights defenders have been harassed and imprisoned," he said in what he called a blog to mark the rights day, citing the case of prominent human rights Nasrin Sotoudeh who was arrested on September 4.
Sotoudeh, renowned for her defence of several offenders on death row for murder under the age of 18 as well as opposition activists, faces charges of acting against the Islamic republic's national security.
But Gass said "her real crime is doing her job courageously and highlighting injustices that the Iranian regime would prefer stayed hidden."
Tehran's ties with London have deteriorated in recent years as Iran accused Britain of backing the anti-government opposition and fomenting unrest after the disputed re-election of President Mahmoud Ahmadinejad in June 2009.
"It is true that part of a diplomat's job is to build bridges where bridges can be built," wrote Gass.
"And diplomats should be cautious in criticising the country to which they are posted. But it is also part of a diplomat's job to explain publicly the views of the government he or she works for."
Iranian leaders have also pointed an accusing finger at the British intelligence service the MI6 as well as US and Israeli intelligence over the assassination of a top nuclear scientist last month.
Dozens of basijis, members of hardline Islamist militia, demonstrated in front of Britain's embassy in downtown Tehran on Sunday over the killing, burning US and British flags, an AFP photographer said.