The deal, which was completed on Monday, included the effective transfer of the SIPPs and SSASs held via the trustee company, Guardian Pension Trustees Limited.
Adam Stephens and Henry Shinners of Smith & Williamson LLP were appointed as joint administrators of GPC on June 11.
Hartley is an established SSAS provider with over 35 years’ experience in the financial services industry, opening its first SIPP in 2001.
It is part of the Wilton Group and manages more than £1 billion of clients’ assets.
Adam Stephens, lead administrator, said: “We are pleased to confirm the sale of the business to Hartley, which will provide continuity of service to GPC’s clients.
“We recognise that the insolvency of GPC may have been unsettling to clients”.
Weightmans LLP acted as legal advisers to the joint administrators on the sale.
James Moore, restructuring and insolvency partner at Weightmans LLP, led the team along with Natasha Atkinson (R&I Partner) and pensions partner Mark Poulston.
The joint administrators confirmed that all staff will transfer across to Hartley, which, they said, should assist in ensuring that clients will experience minimum disruption in the transfer process.
The joint administrators and Hartley “do not anticipate that there will be any interruption to the services previously provided by GPC”.
GPC specialised in the provision of technical and administration services to Guardian Pension Trustees Limited which acted as the corporate trustee of SIPPs and SASSs.
It administered around 3,200 SIPPs and 50 SSASs, holding over 8,000 property assets, and a total investment value of around £130m.
The joint administrators said clients will be contacted “in the coming days” with information about their pensions.