The British messages, which are now classified, are fueling Republican accusations that Mrs Clinton mishandled secret information and therefore "cannot be trusted with the White House".
The controversy continues to dog Mrs Clinton's presidential campaign as the US State Department's releases monthly batches of her emails in response to a Freedom of Information request.
Among the more than 7,000 pages released this week were messages in which Mrs Clinton received a stream of warnings about senior Conservative party figures in the days after they took power in the 2010 election.
Sidney Blumenthal, a longtime friend of Mrs Clinton's and a Labour ally, told the then-US secretary of state to be wary of David Cameron's new government.
"On economic policy, the UK is no partner and no bridge to Europe," Mr Blumenthal wrote six weeks after the British election.
Mr Blumenthal also cautioned Mrs Clinton not to trust William Hague, then foreign secretary, saying he was "deeply anti-European and will be disingenuous with you".
Other messages provided further evidence that Cherie Blair directly lobbied Mrs Clinton on behalf of the Qatari government, and there were consolation emails between Mrs Clinton and David Miliband after he lost the Labour leadership election to his brother Ed.
The emails from Mr Blair, who used an account titled "aclb" - the initials of his full name Anthony Charles Lynton Blair - are largely redacted but appear to include information about a three-hour meeting he had with Benjamin Netanyahu, the Israeli prime minister, in September 2010.
US officials have now classified Mr Blair's emails because they include "foreign government information provided with the expectation of confidentiality". They are due to remain secret until 2035.
Mrs Clinton's campaign argues that the information was not marked classified at the time it was sent and therefore she did not break any secrecy laws.
However, US rules state that some information shared by allied governments is automatically treated as classified and should not be shared by email, regardless of whether it is marked secret.
"It's born classified," J. William Leonard, the former head of classification rules for the US government, told Reuters.
Several other British messages in Mrs Clinton's inbox are now being treated as classified and the information they contain may have been secret from the moment it was shared.
In a January 2010 email, one of Mrs Clinton's aides passed on information from Downing Street about "poisonous" negotiations in Northern Ireland.
Sections of the emails appear to have been redacted because they contain information passed on by the British government in confidence.
A long email sent by an aide to David Miliband, then foreign secretary, includes notes on a 2010 visit he made to Afghanistan. The aide stressed it was for Mrs Clinton's eyes only that Mr Miliband "very much wants the Secretary (only) to see this note".
The message has now been marked confidential by the US government and will not be released until 2029.
Around 125 of the newly-released emails contain information the US government now considers secret, sparking a fresh round of Republican attacks on Mrs Clinton.
"On hundreds of occasions, Hillary Clinton's reckless attempt to skirt transparency laws put sensitive information and our national security at risk," said Reince Preibus, head of the Republican National Committee.
"With the FBI continuing to investigate, Hillary Clinton's growing email scandal shows she cannot be trusted with the White House."
The email controversy appears to have damaged Mrs Clinton politically and a recent poll in three key states found that two in three voters do not believe she is "honest and trustworthy".
Mrs Clinton remains the Democratic front runner and her aides say the email issue has been politicised by Republicans and seized on by the media but is of little interest to the general public.
The emails also show Mrs Clinton requesting skim milk for her tea, asking what time The Good Wife and Parks and Recreation are on television, and inquiring about a shipment of gefilte fish to Israel.
- The Telegraph
