A 61-year-old man was jumped from behind and forced to the ground by robbers who wrestled his bag containing thousands of pounds in cash in Hatfield Road, West Ealing.
The victim was carrying a plastic bag holding around £4,000 when the thugs pounced.
He had visited a bank, which police have decline to name, in Ealing Broadway on the morning of October 4 to withdraw the money which he was use to pay his builder.
The thieves are believed to have followed him from the busy town centre to the quiet, residential street a short distance away, where he was attacked from behind.
He cried out and a brave passer-by rushed to his aid and chased after the thug, but he was unable to catch the robber.
Trainee detective constable Paul Harris, said: "This was a premeditated attack where it appears bank customers were specifically targeted.
"Please be extremely vigilant when withdrawing large amounts of cash and use alternative methods of payment if possible."
Police are keen to speak to the people in the CCTV images about the robbery. Anyone with information should call police on 0300 123 1212 or Crimestoppers anonymously on 0800 555 111.