Update as of 06:19 a.m. EDT: Britain officially reopened its embassy in Tehran Sunday, with a ceremony attended by the country's Foreign Secretary, Philip Hammond.
At the ceremony Hammond said the attack in 2011 had been "a low point" but since the election of President Hassan Rouhani things had "steadily improved, step by step," the BBC reported.
Original story below
KUWAIT (Reuters) - In a signal of the most striking thaw in the Western ties with Iran for over a decade, Foreign Secretary Philip Hammond will reopen the British embassy in Tehran nearly four years since protesters ransacked the elegant ambassadorial residence and burned the Union Jack.
The nuclear deal that the Islamic Republic struck with six major world powers last month has prompted a flurry of European visits - including from German and French ministers - aimed at positioning for the end of Iran's long economic isolation.
But Britain has operated without an embassy since Iranian protesters stormed its two main diplomatic compounds in Tehran on Nov. 29, 2011. The protesters slashed portraits of British monarchs, torched a car and stole electronic equipment.
Following the storming which Prime Minister David Cameron called a 'disgrace', Britain shut the embassy and expelled Iran's diplomats from London. Iran will simultaneously re-open its embassy in London on Sunday, Hammond said in a statement
"Our relationship has improved since 2011," said Hammond, who will be only the second British foreign minister to visit Iran since the 1979 Islamic revolution that toppled the U.S.-backed shah. The last visit was by Jack Straw in 2003.
"Four years on from an attack on the British Embassy, I am today re-opening it," Hammond said.
The statement confirms an earlier report by Reuters on Thursday.
The Tehran and London embassies will initially be run by chargé d'affaires but ambassadors will be agreed with months, Hammond said.
Accompanying Hammond is a small group of business leaders, including representatives from Royal Dutch Shell
"RETURN OF THE FOX"?
After more than a decade of casting the Islamic Republic as a rogue power seeking to sow turmoil through the Middle East, Britain has sought to improve ties with Iran, whose proven natural gas reserves are as vast as Russia's.
"In the first instance, we will want to ensure that the nuclear agreement is a success, including by encouraging trade and investment once sanctions are lifted," Hammond said.
Under the nuclear deal, sanctions imposed by the United States, European Union andUnited Nations will be lifted in exchange for Iran agreeing long-term curbs on a nuclear program that the West thought was intended to make a nuclear bomb.
Tehran has always denied seeking nuclear arms.
Lifting sanctions that prevent Iranian crude reaching the world oil market would open the isolated Iranian economy of 80 million consumers in a way some investors are comparing to the opening up of the Russian economy after the collapse of the Soviet Union in 1991.
"This is a vast emerging market to open up, a vast frontier market: Iran is potentially something of an energy superpower," Norman Lamont, a former British finance minister who now chairs the British Iranian Chamber of Commerce, told Reuters.
"But it is also necessary to be cautious because we do not know quite what American sanctions will remain."
While the nuclear deal is seen as a major opportunity by some, including U.S. PresidentBarack Obama, hardliners in Washington and Tehran have opposed it, as has Israel.
Deep mistrust remains on both sides.
Britain has been cast for decades by opponents inside Iran as a perfidious "Old Fox" or "Little Satan" who does the bidding of "Big Satan," the United States.
An electronic newsletter of the Fars news agency cast the reported re-opening of the embassy as the "Return of the Fox".
Former U.S. President George W. Bush said in 2002 that Iran, along with North Korea andIraq, represented an ‘Axis of Evil’ which threatened the peace of the world.
Iran has provided military and financial support to Syrian President Bashar al-Assad in the four-year-long conflict that has become a focal point for Shi'ite Iran's power struggle with the conservative Sunni Muslim monarchy of Saudi Arabia.
Iranian military support for Assad has come in the form of its backing for the Lebanese political and guerrilla group Hezbollah, the deployment of Iranian military advisers, and the mobilization of Shi'ite fighters from elsewhere in the region.
Britain's opulent 19th Century embassy in Tehran - built as a symbol of imperial might when Britain was locked into the 'Great Game' struggle for influence with swiftly expanding Tsarist Russia - has long been the subject of intrigue.
Following the 2011 storming, which was a protest against nuclear-related sanctions imposed by London, Iranian Supreme Leader Ayatollah Ali Khamenei called it an "evil embassy".
In 2007, Iranian media even claimed to have discovered a secret tunnel running from the embassy under a carpet shop which was used to smuggle "spies and prostitutes".
Protesters in 2011 smashed the large stone lion and unicorn on the gates at the ambassadorial residence, where in 1943 a dinner was held for Winston Churchill, Joseph Stalin and Franklin D. Roosevelt -- the first meeting between the leaders of Britain, Russiaand the United States to discuss their strategy for winning World War Two.
Protesters looted the embassy and smashed some treasures. A portrait of Queen Victoria was torn in two, the head was cut out of a portrait of Edward VII and a picture of QueenElizabeth was stolen.
There has been no U.S. embassy in Tehran since it was sacked in the early days of the Islamic Revolution in 1979 by students who feared a repeat of a 1953 coup when the CIA orchestrated the overthrow of Prime Minister Mohammad Mossadegh.
The U.S. hostage crisis lasted 444 days and Washington and Tehran have never resumed diplomatic relations, leaving Britain first in line for the anti-Western feelings of the hardliners who run the Islamic Republic and their supporters.
(Editing by Robin Pomeroy)