Tony Blair has warned London's mayor about making further big increases in transport fares.
Tony Blair said people must see genuine benefits
The prime minister told BBC London it was important to invest in transport but that Ken Livingstone should be careful not to push people too far.
"If people see genuine benefits then I think they are prepared to make the extra contribution but they need to see it's going to deliver," he said.
Last week the mayor announced fares will rise above inflation in January.
The mayor said the money would be used to pay for a £3bn investment in public transport.
Speaking to Political Editor Tim Donovan, Mr Blair also said investing more money in the police would make a difference.
"When it leads to a more effective economy and where it leads to reduced amounts of crime, it then starts to pay back," he said.
People need to see their money is going to be "wisely and properly spent".
Mr Blair refused to comment on whether he was going to give the mayor more powers but said: "I think he's done a good job and proved himself".