In a statement, the metropolitan police said, "A further arrest has been made in connection with the investigation into the attack on Lt Gen Kuldip Singh Brar in London on September 30.
"On October 10, a 29-year-old man was arrested at a residential address in the West Midlands on suspicion of conspiracy to murder." He currently remains in custody, police said without identifying him.
With Wednesday's arrest, a total of three persons are in custody, two charged with 'intent to cause grievous bodily harm' and one held on suspicion of conspiracy to murder.
The two Indian-origin men charged with causing grievous bodily harm to Brar would appear before a United Kingdom court in London for next hearing on December 7.
Ten others arrested in connection with the attack have been bailed to return in November pending further inquiries.
Brar, 78, who had led Operation Blue Star in 1984 to flush out pro-Khalistan militants from the Golden Temple, was on a private visit here when he was attacked by four men, suspected to be Khalistan sympathisers, while he was returning to his hotel with his wife. He suffered a wound on his neck and cheek but his wife was not injured in the attack.
Brar has since returned to India.