Tony Blair will be remembered as "a successful party leader but not as a good prime minister", Conservative leader David Cameron has said.
Mr Cameron said the Blair years were ending with 'disappointment'
Mr Cameron said the Labour leader had come to power at the 1997 general election "with great hope", but would leave government with "disappointment".
He criticised Mr Blair's handling of the NHS, saying it faced job losses and doctors had been treated "appallingly".
Mr Cameron said voters would have a "choice" at the next general election.
The Tory leader visited Crewe, in Cheshire, as part of the campaign ahead of Thursday's local elections in England.
He said: "Tony Blair's time as prime minister started with great hope but has ended with disappointment.
"It is clear that he has done some good things like making the Bank of England independent.
"But 10 years ago he promised '24 hours to save the NHS'.
"Today, community hospitals face closure, the NHS faces more job losses than ever, maternity units are under threat, it is difficult to find an NHS dentist, and junior doctors are being treated appallingly."
Earlier, Mr Blair said that "in all probability" Chancellor Gordon Brown would succeed him as prime minister "in the next few weeks".
He added that Mr Brown was "someone who has built our economy into one of the strongest in the world, and who, as I have said many times before, would make a great prime minister for Britain".
The chancellor is expected not to face a Cabinet-level challenge for the Labour leadership when Mr Blair steps down later this month.
Speaking during a visit to Leighton Hospital in Crewe, Mr Cameron said "Tony Blair has been casting around for ages for somebody else to do the job but he couldn't find anybody.
"People in Britain should have a choice at the next election and that's what I intend to give them."
In a speech earlier, Mr Blair said 10 years of Labour government had left the UK stronger, fairer and better. He has also hailed the improvements Labour has made to the NHS.