Five men and one woman have been arrested. Three suspects are being held in custody to appear before magistrates today.
The investigation relates to a suspected advance fee and commercial rent fraud.
Gresham Ltd and Gresham Finance (London) Ltd offered loans of up to £250m and applicants were charged between £5,000 and £50,000 for due diligence checks. Applicants were then asked to pay a security deposit of between 1 and 5 per cent of the loan amount.
Most of the applications were from overseas commercial projects for resorts and hotels in Austria, Turkey and other countries.
The searches of residential and commercial properties in London, Surrey, Cheshire and Derbyshire involved more than a hundred investigators and police officers.
The SFO says the swoop was intended to prevent further losses to the victims.
The SFO says the same suspects were involved in a retail property renting business operating as Gresham Ltd, Park Regent Ltd and Castlereagh London.
The suspects also used a complex array of company names in their dealings, including 45 Oxford St Ltd, Alliance Trust, Renaissance Trust, Cutting and Company (Investments) Ltd and Paul Street Media Ltd.
The Fraud Office points out there is no connection with Gresham Finance Ltd or Castlereagh Ltd of Dublin,which are not under investigation.
The SFO also points out that Alliance Trust is not to be confused with the Alliance Trust Plc, the FTSE 100 firm, which is an unconnected company and also not under investigation.