SAS, special forces in the British Military. They are very good.

Left: The burnt-out embassy after the siege. Photo Credit. Right: SAS during assault on the embassy.
On 5th May 1980, the Special Air Service (SAS) stormed the Iranian embassy in London, ending a six-day siege. It was an event that brought together two significant trends of the 20th century – the growing importance of specialist units such as the SAS, and the increasing prevalence of news media directly reporting on military action.
The Embassy Siege

The front of the Iranian embassy in 2008. Photo Credit.
On the 30th April 1980, six armed men entered the Iranian embassy in London. Its inhabitants were taken hostage – staff and guests who included the ambassador, British journalists and PC Trevor Lock, the policeman guarding the embassy.
The terrorists were members of the Democratic Revolutionary Front for the Liberation of Arabistan, a group fighting for independence from Iran for their home region. They demanded the release of prisoners held by the Iranian government.
Read more at: https://www.warhistoryonline.com/history/operation-nimrod-iranian-embassy.html
One hostage was killed, a number of terrorists killed, no SAS members were killed. It was a successful mission despite 2 hostages suffering serious injuries.