The action is part of an investigation by HMRC in close co-operation with The Pensions Regulator and the FSA.
Fourteen premises were searched including residential addresses in Merseyside, Greater Manchester, Staffordshire, Worcestershire and Cumbria.
Documents, paperwork, mobile phones and computers were seized. The individuals have been questioned.
HMRC assistant director criminal investigations North West Mike O’Grady says: “This is an unusual investigation into what we believe to be an organised attack on tax relief available on self-invested pension schemes.
“We do not expect to know the full scale of this suspected fraud until we have assessed all the evidence collected.”
The arrests follow an investigation by HMRC officers into the suspected fraudulent use of tax relief repayments linked to pension schemes marketed by a number of UK financial firms.
The case involves the suspected fraudulent reclamation of income tax relief on pension contributions contrary to the pension tax rules under Part 4 of the Finance Act 2004.
FSA small firms division head of investments Linda Woodall says: “We have been working closely with HMRC and the TPR on this matter and are monitoring the financial firms involved.
“We will take action if it is appropriate to do so within our remit as a financial services regulator.”