Sir Scott Baker says there is not a “tissue paper” between the way the treaty works in both countries.
He told MPs there were human rights issues affecting the extradition of alleged hacker Gary McKinnon.
And he also called for “inconsistencies” in the European Arrest Warrant system to be remedied.
MPs on the Commons Home Affairs Committee told Sir Scott that ministers including the Attorney General Dominic Grieve had seen his findings as “just another report” and that the deputy prime minister Nick Clegg was clearly “unhappy”.
But Sir Scott refused to be drawn: “We have produced our report, it’s up to the politicians to do what they want with it.”
David Cameron criticised the Extradition Act 2003 when in opposition and the review follows widespread concern that the system is biased against Britain.
Critics argue it is unfair for the US to require “sufficient evidence to establish probable cause” before agreeing to extradite anyone to the UK, while Britons are denied the same protection.
But despite repeated questions from MPs on the committee Sir Scott insisted there was no practical difference between “probable cause” and the UK requirement to allow extradition on “reasonable suspicion”.
Gary McKinnon case
The committee’s Labour chairman Keith Vaz said for the public the two phrases were very different.
“One is about suspicion the other is about belief,” he said. “In normal ordinary language if you suspect something it’s quite different from believing something surely?”
But Sir Scott disagreed: “The test in the Act, you couldn’t put a sheet of tissue paper between that and the test the other way for extradition from the United States.
“Nobody has drawn our attention to any single case at any stage… where it would have made any difference whether you applied the American test or the United Kingdom test.
“There are very serious delays and we get our people a lot quicker from there and than they get theirs from us.”
The Home Secretary Theresa May is currently considering the case of Gary McKinnon, who has Asperger’s syndrome, and is accused of hacking US military computer systems.
But Sir Scott says because human rights issues have been raised in his case, it should be decided “back in the courts” not by the Home Secretary.
“That would have the advantage of resolving the issue much more speedily and it would also avoid the endless further steps of the Secretary of State being judicially reviewed. It also takes the Secretary of State out of the political arena.”
On the European Arrest Warrant system which Sir Scott also reviewed, he said although it broadly worked well there were “very serious problems” in a “handful of cases” which needed to be remedied.
But he cautioned against a wholesale review.
“Once you start chipping away at the framework decision, if you are not careful the whole thing falls apart,” he said.