Police took bicycles off passing cyclists to help them run down a suspected criminal in Cambridge on Monday.
Officers were following a man who had threatened staff at Marks & Spencer by patrol car, but were at risk of losing sight of him.
So they hailed two members of the public, borrowed their bikes and hot-pedalled it to catch the man and make an arrest.
Sgt Nick Ashton-Jones, one of the officers who gave chase, told the Cambridge News: “This was an incredibly selfless and public-spirited act.
“My colleague and I may not have caught up with the man had it not been for these two members of the public and I'd like to tell them how grateful I am.”
Both bicycles were returned to their owners and a 35-year-old man from the Cambridge area was arrested on suspicion of theft and possessing an offensive weapon. He has been detained under the Mental Health Act.