Only one crime was solved by each 1,000 CCTV cameras in London last year, a report into the city's surveillance network has claimed.
The internal police report found the million-plus cameras in London rarely help catch criminals.
In one month CCTV helped capture just eight out of 269 suspected robbers.
David Davis MP, the former shadow home secretary, said: "It should provoke a long overdue rethink on where the crime prevention budget is being spent."
He added: "CCTV leads to massive expense and minimum effectiveness.
"It creates a huge intrusion on privacy, yet provides little or no improvement in security.
"The Metropolitan Police has been extraordinarily slow to act to deal with the ineffectiveness of CCTV."
Nationwide, the government has spent £500m on CCTV cameras.