A £600,000 bronze sculpture, which would have taken "at least eight people" to carry, has been stolen from the grounds of a university.
The sculpture is part of a series of three
Lynn Chadwick's two-metre piece The Watchers was taken from Roehampton University in south-west London overnight on 10 January.
Six weeks ago a £3m Henry Moore bronze was taken from the Henry Moore Foundation in Hertfordshire.
Police said 20 art thefts had happened in London in the past six months.
Officers fear thieves are targeting valuable artworks worth millions of pounds so they can melt them down and sell them on as scrap metal at a fraction of the price.
Chadwick, who was born in London in 1914 and died in 2003, won the International Prize for Sculpture at the XXVIII Venice Biennale in 1956 and was awarded the CBE in 1964.
Detective Sergeant Vernon Rapley, head of the Metropolitan Police's arts and antiques unit, said: "The people perpetrating these crimes appear to have no appreciation of, or respect for, the objects they are stealing.
"Rewards have been offered for the return of some of the objects and we would encourage anyone with information to come forward and assist us to recover these important objects."
The Watchers is one of a series of three sculptures by Chadwick - the other two are in Loughborough and Denmark.
The Henry Moore sculpture was stolen by thieves using a flat-bed truck with a crane on the back.