"Officers from the MPS have this evening arrested three men and one woman on suspicion of conspiracy to murder in connection with the investigation into the attempted murder of an Indian man (Brar) in central London on September 30," a spokesperson of the Metropolitan Police Service told .
"All the four are being taken to a central London police station where they will be interviewed by detectives," he added.
In the first arrest, one 33-year-old man and a 40-year-old woman were held from Wolverhampton at about 17:00 BST, the spokesperson said.
Another 34-year-old man was arrested after being stopped in a car in West Bromwich about 30 minutes later, while a 25-year-old man was arrested in the same circumstances at 19:00 BST, he said.
"All four are being taken to a central London police station where they will be interviewed by detectives. Inquiries are ongoing and police continue to appeal for information into the incident," he said.
Brar (78) was on a private visit when he was attacked by four men in Old Quebec Street near Oxford Street on Sunday night when he was returning to his hotel with his wife.
Brar, who was assaulted with a knife or a sharp implement, suffered a wound on his neck but his wife was not injured in the attack, police had said.
The four men who attacked him were described as being of Asian appearance, all with long beards, and were wearing dark clothing and long black jackets.
One was described as younger and slimmer than the other three. They all fled in the direction of Oxford Street.
After the attack, Brar said he had informed local army authorities in Mumbai about his private visit to London, but the Indian High Commission here said it was unaware of his trip.
Brar, who returned to Mumbai along with his wife after receiving initial treatment, had said that he is convinced it was an attempt to assassinate him by "pro-Khalistan elements" for his role in the 1984 'Operation Blue Star'.
"There were lot of hate messages on the net, there were online threats against me. There were pledges to kill me," he had said.
The operation was aimed at flushing out Sikh terrorists led by Jarnail Singh Bhindrawale from the Golden Temple.General AS Vaidya who was the Army Chief in 1984 planned the highly controversial 'Operation Blue Star'.
In 1986 Vaidya was shot dead in Pune.