Detectives are investigating one of Britain’s biggest buy-to-let schemes in which large numbers of investors have seen their savings wiped out.

They fear thousands of people who sought to cash in on the buy-to-let dream during the boom years of 2004 to 2007 may turn out to have been victims of organised fraud.

The Serious Fraud Office (SFO) is investigating alleged scams that have cost government-owned banks such as Northern Rock, Royal Bank of Scotland and Bradford & Bingley millions of pounds on loans that should never have been made.

Senior police officers said the full scale of the buy-to-let scandal was only beginning to emerge in the wake of the credit crunch and the collapse of house prices.

One chief constable said: “We can expect to see one or two of the same type of [scheme] emerging in every major city.”

The SFO said last week it was investigating two alleged buy-to-let frauds, involving properties in Leeds, Cardiff, Nottingham, Derby, Liverpool, Hull, Newcastle upon Tyne, Glasgow and London. Police in Greater Manchester, the West Midlands, and West Yorkshire are also involved in the inquiries.

At the centre of one of the biggest police investigations is Morris Properties, which specialised in student new-build flats and refurbished homes in Leeds and the northeast. It sold 1,000 properties before going bust last summer.

The firm was established by Simon Morris, a local developer who built up a £69m fortune by selling buy-to-let properties.

Morris’s firm lured investors with promises of substantial “discounts” on flats that were allegedly overpriced, and guaranteed rental income, which in many cases failed to materialise. Investors, drawn in by the mirage of ever-increasing house prices, were easy prey.

With property prices now falling in some areas by as much as 50%, many of those investors are facing ruin. The victims include doctors, nurses, teachers and builders who have seen portfolios worth hundreds of thousands of pounds vanish. Many have had their properties repossessed or been forced to sell at knockdown prices.

A whistleblower who once worked for Morris and fell into debts of £500,000 after making buy-to-let investments with the firm said he had received threats after helping the police. Morris denies any wrongdoing.

Last week Morris was accused by lawyers representing 133 of his former clients of overseeing a scheme in which flats were sold to innocent investors for as much as 100% above their real value.

Hammad Ahmad, a solicitor with Max Gold Partnership, said his clients would launch a group legal action in the new year against the Morris companies and several conveyancing solicitors and valuers involved in the sales.