The tracking of terrorist assets... demands the same kind of sophistication as was brought to bear to break the Enigma codes

Gordon Brown Chancellor of the Exchequer

"Let me put it affirmatively: I have no idea how much is out there, how much more there is to do," he told reporters.

"There's never been an attempt like this taking in all the countries of the world, so we're on a mission without clarity about how large the funds are."

Getting better

But he stressed that progress is being made, and lessons learnt.

"Before 11 September we did not do as good a job as we need to do in deploying intelligence assets so that we can identify probable (terrorists) and go after them," Mr O'Neill said.

"Since then we've learnt, we've done an incredible job in refocusing on proven and probable terrorists, against the backdrop of a process that goes on without end."

The sums frozen - about $10m in the UK, $34m in the US and $60m elsewhere - were dwarfed by the probable sum total of terrorist finance, and represented what was left in accounts when they were tapped.

But Mr O'Neill said the important thing was that the authorities are "disrupting the channels".

Tracing the money

Both the US and UK will continue to pressure other countries to catch up, Mr Brown added.

Frozen funds

189 individuals & organisations named 142 countries have frozen accounts $104.8m blocked ($34.2m in US, $10m in UK, $60.5m elsewhere)

Of the 150 governments which have frozen funds since 11 September, only 58 have established institutions to trace money.

"We can only be as strong as our weakest link," Mr Brown said.

He acknowledged the difficulties facing, for instance, financial institutions trying to track the money.

"The money may well be from a legitimate source, and that makes life very difficult for financial institutions, because you're asking them to do more to identify suspicious transactions," he said.

BBC News Online has been told by police and financial sector sources that before 11 September, the co-operation between police, intelligence and the private sector - and the resources available for terror funds - were inadequate.

Big push

Mr Brown said the lessons had been learnt - and compared the need for new skills to the massive civilian and military push during World War II to break enemy codes.

"What we are learning is that we've got to learn new methods," he said.

"The tracking of terrorist assets by financial intelligence, by forensic accountancy, working with private sector skills as well as traditional public sector ones, demands the same kind of sophistication as was brought to bear to break the Enigma codes.

"It's that level of sophistication that we're trying to develop right across Europe. I'm sure there's a generation of people coming out of our universities as well as in professions who want to play a part."