The HSBC files, the biggest banking leak in history, reveal the full scale of malpractice at its Swiss subsidiary. Recent court cases in the US and Europe have provided individual examples of the bank’s wrongdoing, but the leaked files show how these cases were part of a persistent pattern of misconduct.

In one case that illustrates the bank’s conduct, a wealthy British client, Stoke City football club director Keith Humphreys, frankly told his HSBC manager that his father’s $430,000 (£280,000) Swiss account was “not declared” to the UK tax authorities.

Humphreys, whose wealth originated from the sale of a local supermarket chain, explained that one HSBC manager had already advised how to extract undeclared offshore money via a credit card.

“The credit card is thus used to enable the Humphreys family to make withdrawals from ‘cash points’ when they are outside the UK,” he said.

The banker, who even brought paperwork to Humphreys’ stately home in Cheshire because the client was uneasy about “walking around with a set of account-opening documents”, recorded how Humphreys was also alarmed to hear a Swiss lawyer might realise he had a secret HSBC account. “This situation initially appeared to cause some disquiet to my hosts, though this later gave way to a more relaxed attitude with the sentiment that Genevan lawyers would be discreet, something that I did nothing to discourage.”

On clinching arrangements in London, the bank manager wrote: “We subsequently repaired to the Ritz, for a very enjoyable lunch.” Humphreys told the Guardian his father eventually had to repay about $224,000 (£147,000) for evading tax due to the UK.

Another customer, retired accountant Andrew Sebastian, also told the Guardian how he had now been made to pay about $64,000 (£42,000) in back tax, interest and penalties. HSBC in Switzerland had supplied him with £50,000 in sterling banknotes in the course of a year.

Facebook Twitter Pinterest HSBC files: how secret Swiss account data detailing misconduct came to light.

At its height, HSBC’s secretive Swiss arm hid a total of $120bn (£78bn) in assets. These funds were collected from wealthy clients all over the world and have already led to criminal investigations and charges against the bank in France, Belgium, the US and Argentina. But in Britain, no legal action has been taken against HSBC and the evidence against it had never been made public until now.

The leaked Swiss HSBC files implicate the bank in apparent misbehaviour all over the world. One Australia-based HSBC client planned to share his “black” account with his daughter in London.

The bank noted: “The account is ‘undeclared’, a fact with which [she] may not be entirely at ease – as a compliance officer at Kleinwort Benson.” The manager wrote that the account was also not declared “to the best of my knowledge” to the tax authorities in Australia.

HSBC was so keen to protect its clients that it used a codename when phoning another prominent Australian financier, Charles Goode, then chairman of the ANZ bank in Melbourne, about his US$318,000 deposit. According to the files, HSBC instructed he “would like to be called Mr Shaw”. Goode told the Guardian the use of a codename was the bank’s idea, not his, and the deposit had long been left dormant by him. He says he has paid all tax due on the account.

Another HSBC manager wrote on the file of Irish businessman John Cashell (later to be convicted of a tax fraud): “His preoccupation is with the risk of disclosure to the Irish authorities. Once again I endeavoured to reassure him that there is no risk of that happening.”

HSBC similarly recorded on the file of a British property developer: “He is very much concerned that … client information could be exchanged … I explained [to] him that we are bound to CH [Swiss] banking secrecy, which is one of the strictest in the world.”

HSBC appears to have allowed executives of a textile firm to conceal unregistered “bearer share” certificates in a Swiss safe, which would have revealed who really owned the company. Bearer shares are banned in some countries because of their potential for abuse.

The bank recorded: “In this safe are some very important documents (bearer share(s), which belong to the beneficial owner Mr DL from Israel. These shares are kept in a safe for tax reasons.”

In a separate transaction, the bankers themselves recorded that they were uneasy when a Serbian businessman wanted to deposit €20m (£15m). But they merely asked him to act less conspicuously.

HSBC “explained that as per today the bank did not interfere in his money transfer transactions but would have preferred to reduce those activities on a lower scale. [He] understands our concerns and will use smaller amounts”.

The bankers seem to have been reluctant to take risks personally. The files record that a wealthy owner of a London furniture store and holder of a secret HSBC Swiss account, demanded HSBC “help him get back money into the UK on a ‘non-declared’ basis” by carrying in bundles of cash.

HSBC offered instead to provide him or a colleague with sterling banknotes in Switzerland, recording, “what he decided to do with friends of his … was his affair”. In a revealing remark, an HSBC manager wrote on the files: “We made clear the difference between passive and active action on our part.”

This tax evader also ended up repaying UK authorities, as part of a $205m (£135m) haul Britain has so far recovered from HSBC’s tax-dodging customers. Chris Meares, then overall head of HSBC private banking, assured the Treasury committee in 2008: “We prohibit our bankers from encouraging or being involved in tax evasion.”

But former tax inspector Richard Brooks, author of The Great Tax Robbery, who is interviewed about HSBC on BBC Panorama on Monday night, says: “I think they were a tax avoidance and tax evasion service. I think that’s what they were offering. They knew full well that people come to them to doge their tax liabilities. There are very few reasons to have an offshore bank account, apart from just saving tax.”

The HSBC files are being published in an international collaboration including the French daily Le Monde in Paris, which first obtained the data; the Washington-based International Consortium of Investigative Journalists; and BBC Panorama.

HSBC says it won’t comment on many of the specific allegations because of ongoing criminal investigations and because of Swiss bank secrecy laws.

But HSBC also says it has now embarked on a radical cleanup of its Swiss act. It says it has not only introduced “strict controls” on cash withdrawals, but also ended the “hold mail service” (the practice of not sending giveaway letters to customers’ home countries); and got rid of 70% of its previous customers.

“HSBC has implemented numerous initiatives designed to prevent its banking services being used to evade taxes or launder money.”