LONDON- The UK Serious Fraud Office (SFO) said on Wednesday one person had been arrested and properties across Britain raided in an investigation into a 150 million pound ($205 million) investment scheme that targeted 1,500 people from 50 countries.

The SFO said it was investigating the Alpha and Green Park group of companies for suspected money laundering and fraud. Two directors of the companies, which promised annual 8-10% returns on investments in student accommodation and holiday parks, might have made about 20 million pounds, it said.

But investors stopped receiving their "guaranteed returns" in 2018, the SFO said in a statement.

The fraud agency said that after a six-month investigation it had carried out a series of co-ordinated raids, interviews and mandatory requests for evidence and said it suspected investors had been fraudulently misled.

Reuters was not immediately able to contact the companies, or their legal representatives, for comment.

Mick Gallagher, the SFO's chief investigator, called on anyone with a connection to the investigation to step forward. All UK-based investors will be asked to fill out a questionnaire by end-November as part of the inquiry. ($1 = 0.7311 pounds)

(Reporting by Kirstin Ridley; Editing by Alexander Smith) ((; +44 (0) 207 513 5666;))