It was the death threats that set Monticello apart.

In the late 1990s, share ramping was an ongoing problem. Unsubstantiated rumours about certain companies would appear in internet chatrooms and share prices would rise and fall dramatically.

Monticello plc, which launched at the height of the dotcom boom, was an extreme example. In January 2000, the company’s chief executive, Mark O’Hanlon, gave an extensive and highly misleading interview to a now defunct news site about Monticello’s prospects.

Its share price immediately soared. The shares were suspended from Ofex – the unregulated share market – then relisted, then barred altogether. As a consequence, dozens of shareholders lost their entire investment in the company. A court was told that “many investors had lost a very considerable sum of money”.

After an inquiry by the Department of Trade and Industry (DTI), O’Hanlon pleaded guilty to a single count under section 47 of the Financial Services Act 1986 of making a misleading, false or deceptive statement or forecast. He was sentenced to 18 months in jail.

One of the key witnesses has told the Guardian he was repeatedly threatened in the run-up to his appearance in court. He says he was told his house would burn down.

In an entirely separate investment scam, Monticello’s company secretary Andrew Sommerville was banned from being a director for 12 years.

Though the rise and fall of Monticello has been consigned to history, not everyone got dragged down with it.

The Guardian can now reveal that one of the main players at Monticello was Amber Rudd.

Now the UK home secretary, Rudd was the company’s investment relations officer, which meant she was responsible for maintaining relationships with shareholders as Monticello’s share price moved erratically as a result of the illegal price ramping.

However, Monticello was only one of a series of unlikely steps in the home secretary’s career.

On the Home Office’s website, in a summary of Rudd’s previous career, she is listed as working in investment banking – a stint at JP Morgan – before moving into venture capital.

“She then set up a freelance recruitment business and wrote for financial publications, before being elected to parliament,” it concludes.

However, the reality is rather more complicated than that.

Born in 1963, Rudd was educated at Cheltenham Ladies’ College, Queen’s College in London and then Edinburgh University. But she soon moved into the world of venture capitalism.

Rudd was in her early 20s when her stockbroker father, Tony Rudd, was first investigated by the DTI. It was 1986, and the DTI petitioned for the winding up of Buckingham Corporate Securities, a company based at offices occupied by Tony Rudd and an investment company, Lawnstone.

The DTI also investigated another company, Norton Group, which was also connected to the Rudd family. A third investigation by the DTI into a different investment trust labelled Tony Rudd and his business partner as “totally unfit to be directors of a company”.

In the late 1980s, Amber Rudd and later her mother, Ethne, became directors of the Lawnstone investment company, which continued to make payments to her father for consultancy services.

The 1988 accounts for Lawnstone also show the company issuing a loan note of £100,000 to Amber Rudd. It is unclear what happened to the loan.

Despite her father’s troubles with investigators, the future MP was not put off. By the time she was 31, she was the executive director of a company called Kensington Resources, which was prospecting for diamonds in Canada.

By 1994, a second company called Siberian Pacific Resources – funded by Zvi Alexander, who was then a key player in the Israeli oil industry – had managed to obtain Russia’s first issued licence to mine for diamonds. Rudd had raised 500,000 Canadian dollars to hunt for diamonds in the Krasnoyarsk region.

By the end of the year, Siberian Pacific Resources was approved for listing on a Canadian stock exchange. The company was not a success. Alexander has written that it was “an interesting project with great potential”.

But he concludes: “The economic collapse in Russia in 1996 put an end to this effort as well.”

By February 1996, a new company was incorporated, with Rudd as a director and a shareholder. This company was Zinc Metallurgical Products. The plan was to develop a revolutionary way of extracting zinc from ore in Peru.

Rudd’s mother and Lawnstone Securities also invested in the new technology. Other shareholders included the Earl of Woolton and Lord Marland, a former Conservative treasurer.

In October 1997, the company – now called The Zinc Corporation – tried to float on Ofex.

It needed to accumulate £500,000 of investment in order to list on the market, but in a bizarre episode, it lost a key £12,500 cheque from one investor. It was therefore unable to launch, and this meant that all the other cheques had to be returned.

At the time, Rudd said: “After much soul-searching and a lot of legal advice, we decided to take the ultra-conservative route and return all the money.”

Unfortunately, the zinc extraction did not come to fruition either.

The annual report for the year ending 1999 shows that the company had made a loss of £498,043.

In January 1999, Monticello made an offer for the company, which is how Rudd came to be involved with O’Hanlon.

Set up at the peak of the dotcom boom, the plan was that Monticello would identify startup internet businesses. It would offer them accommodation and business services in return for a share of the equity in those companies, typically 15%.

The calculation was that many of the businesses would fail, but from time to time there would be a success story.

Rudd became a director of Monticello – named after the Georgian house in Russell Square in London where the company was based – in May 1999. It began to develop its business strategy. However, after O’Hanlon’s disastrous interview in early January, the company began to flounder.

In May 2000, Rudd stepped down from Monticello, and the company was struck off soon after. The complex case took several years to come to court, and one of the key witnesses said that he received a series of death threats over the telephone from male voices over that period.

A spokesperson for the home secretary said: “It is a matter of public record that Amber had a career in business before entering politics. Monticello was thoroughly investigated 16 years ago and those who acted wrongly were identified and prosecuted.”

At the same time as she was a director at Monticello, Rudd was also involved in a Bahamas company called Advanced Asset Allocation Fund, becoming a director in December 1998.

She was also a director of another Bahamas company, Advanced Asset Allocation Management, which is revealed for the first time in the Bahamas leaks.

She left this company two days after she stepped down from Monticello.

During this time, Rudd was also involved in several other business plans, including raising money for a suit designer and a headhunting company.

She was also the “aristocracy coordinator” for the film Four Weddings and a Funeral, which led to an unlikely business of hiring out “posh” friends to raise the social tone at events.

Rudd told Harpers & Queen that her contacts “might well be more than happy to attend genuine weddings” for £100 a day. The advantage was that they owned “their own morning dress”.

In 1990, Rudd married AA Gill, the Sunday Times columnist. They split up in 1995, when he began a relationship with the model Nicola Formby.

Amber Rudd’s brother, Roland Rudd, is one of the leading PR executives in London, who runs Finsbury.

Eventually, Rudd decided to put her business career behind her. In 2005, she stood for the Tories in the safe Labour seat of Liverpool Garston, and in 2010 she was elected as Conservative MP for Hastings and Rye. She was appointed home secretary in July.