Experts say countries must co-operate more
Metropolitan Police commissioner Sir John Stevens also said the 11 September terror attacks were a "wake up call" on how security services monitor the activities of extremists.
He said British police had not been warned that suspected shoe bomber Richard Reid was a potential security risk.
"We have to make sure that our relationships with other law enforcement agencies around the world in terms of our war against terrorism are better," said Sir John.
"We know we've got a problem with worldwide terrorism and we've got to act on it."
'Intelligence is power'
Experts said there had been improvements in co-operation between agencies since 11 September, but there were still serious hurdles.
"Intelligence is power and there are still tremendous problems between European countries.
"Inside a country there is always politicking between the external and internal agencies over budgets, jurisdiction and personalities."
Foreign Secretary Jack Straw said a full review would be carried out on both sides of the Atlantic to learn lessons from the terrorist incidents.
He said he doubted if more could have been done to stop Richard Reid.
Mr Stevens told the BBC Radio 4'sToday programme: "If you are asking me if, in a perfect world, could this man have been discovered, I expect in a perfect world he could have been.
"But if you are asking me whether in the world in which we live, on the information I have, more could have been done, I doubt it.
'Wake-up call'
"We are at the highest state of alert that we have ever been from Real IRA terrorism, domestic terrorism, and we're certainly at a high state of alert in relation to international terrorism," the commissioner added.
His comments came after a senior member of the Metropolitan Police Authority admitted police may have ignored warnings that extremists were recruiting from London mosques.
Peter Herbert, the authority's deputy chairman said it was possible mistakes had been made.
But Home Secretary David Blunkett earlier challenged claims that government complacency had allowed radical Muslim clerics to recruit converts to Islamic extremism in Britain.
Mr Reid, who worshipped at a Brixton mosque, is due to appear at a US court on Friday after allegedly trying to set off a bomb in his shoe on an American Airlines Paris-Miami flight.
Mr Stevens told BBC Radio 4's Today programme: "11 September was a wake up call in terms of the fundamental ways we deal with things in religious terms."
"Before 11 September we kept a watching brief on these particular people with MI5 and MI6.
But he said since then there had been a "heightened awareness".
He continued that there needed to be more police officers from ethnic minorities to successfully infiltrate groups targeted by extremists seeking recruits.