You're a billionaire but you don't want anyone, least of all the taxman, to know. What do you do? Head for a palm-fringed island paradise or a snow-covered Alpine micro-state?

Wrong. The world's most opaque jurisdictions – the ones that will best shield you and your cash from the light – are mostly in the heart of the most sophisticated and powerful global financial centres.

London, Luxembourg and Zurich are in the top five most secretive jurisdictions, according the first comprehensive index of financial transparency ever compiled. Yet top of the pile, beating the British Virgin Islands, Belize or Liechtenstein as the best place to hide wealth, is Delaware.

One of the smallest states in the US, it offers the best protection for anyone who does not want to disclose their identity as a beneficial owner of a company. That is one very good reason why the East Coast state hosts 50% of the US's quoted firms and 650,000 companies – almost equivalent to one company per Delaware resident.

The Financial Secrecy Index took 18 months to compile, was researched by senior academics, accountants and investigators under the banner of the Tax Justice Network, and runs to 1,800 pages. It uses findings from the Financial Action Task Force, the high-level global body combating money laundering and terrorist finance, and the International Narcotics Control Strategy Report, as well as 12 key indicators involving bank secrecy rules, disclosure of beneficial ownership and trust law.

It finds that Delaware – the political power-base of the US vice-president, Joe Biden – offers high levels of banking secrecy and does not make details of trusts, company accounts and beneficial ownership a matter of public record. Delaware also allows companies to re-domicile within its borders with minimal disclosure, and allows the existence of privacy-enhancing "protected cell" or "segregated portfolio" companies, among many other stratagems useful for protecting the identity of those who do business there.

The only financial privacy indicator on which Delaware scores positively is that it is party to a large number of international tax information sharing agreements, but this is because those agreements are signed by the United States.

Delaware state officials say it is not the ability to protect identities that attracts so many companies and individuals to register businesses; rather, it is the state's sophisticated judicial system, which has evolved, they say, into the top corporate dispute resolution centre in America.

But lawyer Jack Blum, a former US Senate staff attorney who has worked on high-profile fraud cases, including the BCCI investigation, says: "Secrecy in Delaware has been a massive problem and has been for sometime. They have a lot of rules that… make it so advantageous to be there that it is breathtaking." And, he adds, requests for legal assistance from other countries fall on deaf ears. "The requests pile up in district courts. It's beyond embarrassing. It's a disgrace."

Delaware's top position in the index will be greeted with raised eyebrows in Switzerland, which has just emerged from a bitter two-year legal dispute with the US over Swiss bank UBS's role in facilitating tax evasion on a vast scale.

Both jurisdictions are joined in the top five by the UK. Though Britain does not have many of the features of a secrecy jurisdiction – for instance, accounts are publicly available and companies cannot change their domicile without trace – London has been dragged into the list because of its sheer scale as a financial centre and its capacity to facilitate money-laundering and terrorist finance.

In a devastating appraisal of the UK's financial investigation powers, the Financial Action Task Force, in its most recent assessment two years ago, stated: "There are not adequate measures in place to ensure that there is adequate, accurate and timely information on the beneficial ownership and control of legal persons that can be obtained or accessed in a timely fashion."

Not surprisingly, representatives from the Caymans and Luxembourg, which made it into the top five, are aggrieved at their inclusion. Anthony Travers, chairman of Cayman Finance, the islands' business representative body, says: "Anybody who claims to have evidence that Cayman is opaque hasn't read the IMF and Financial Action Task Force reports nor the US version from the General Accountability Office... [This] report [has a] selective bias and [is] totally discredited, and will be seen as such by everybody in the financial world."

Luxembourg's Association of Banks & Bankers (ABBL) takes a similar line: "The ABBL does not consider Luxembourg to be a 'secrecy jurisdiction'. In both penal and fiscal matters, Luxembourg already co-operates more fully on an international basis than 80% of countries in the world."

But John Christensen, a director of Tax Justice Network and a joint author of the report, says: "The secrecy jurisdictions are found in North America, the former British empire and Europe. These are the regions which have driven the neo-liberalisation project that has skewered financial markets and turned them into criminogenic markets. They can attract capital with no questions asked. What this reveals is the massive hypocrisy of OECD states."

The world's most powerful countries will aim to clamp down further on offshore tax havens at the G20 finance ministers' meetings in Scotland later this month. The question of whether they should extend the measures they take to their own jurisdictions will not, in all likelihood, be on the agenda.

The top five secrecy jurisdictions

Delaware, US: The world's top secrecy jurisdiction. Register a company here and no one will ever know. If you have overseas income, it will be tax exempt.

Luxembourg: Europe's most powerful investment management centre. It does require company accounts to be publicly available. But in virtually every other category secrecy rules.

Switzerland: The traditional home of the opaque bank. For years, it resisted international requests for tax information exchange.

Cayman Islands: The Caribbean island has a serious budget crisis. Its leaders take a dim view of having the "good name" of the most powerful hedge fund centre tarnished by accusations.

City of London, UK: The International Narcotics Control Strategy Report said last year: "Illicit cash is consolidated in the UK and then moved overseas where it can readily enter the legitimate financial system." It adds: "Drug traffickers and other criminals are able to launder substantial amounts of money in the UK despite improved anti-money laundering measures."