By Frances Harrison
BBC News, Tehran
Demonstrators have thrown paint and eggs at the UK embassy in Tehran to try to prevent an annual party in honour of Queen Elizabeth II's birthday.
The protesters said the UK envoy must be expelled
They said any Iranian guests who tried to attend the party were dirty traitors willing to sell out their country.
The protesters also called for the expulsion of the ambassador and relations to be cut off.
Police beat back demonstrators as they tried to block the mission's side entrance to stop guests from entering.
This is the first time protesters have tried to sabotage an embassy reception like this, and it stems from a desire to stop Iranians having contacts with foreigners.
"The British embassy should be shut down" and "Death to England, down with the den of spies," the demonstrators shouted.
Riot police tried to push the protesters away from the mission
All this as 1,500 guests were invited for the biggest diplomatic reception of the year at the embassy.
Islamic students in black shirts pelted the front gate of the building with bags filled with coloured paint, tomatoes and eggs.
"Shame on you, servants of the English," they chanted.
They called the guests dirty Iranians willing to eat the birthday cake of the queen of lies and corruption.
The women demonstrators screamed as the riot police pushed and shoved them to try to make them leave.
The police chased away journalists as they did not want to be seen beating their own people to defend a foreign embassy.
Some diplomatic cars turned back as they saw how volatile the situation was.
At least one vehicle was attacked, and many guests gave up trying to go to the party after getting stuck in traffic.
A couple of hundred determined guests did make it inside the compound.
But the intention was to intimidate Iranians from attending.
This comes as Iran's minister of intelligence recently warned Iranians not to give interviews or information to foreigners, and a number of Iranian-Americans have been jailed on suspicion of spying.
Queen Elizabeth II was born on 21 April 1926, but official celebrations to mark her birthday are held in June.