The investment, which was designed for healthcare social enterprise Urgent Care, is repaid as an agreed percentage of future annual gross revenues.
Urgent Care provides responses to non-emergency 999 calls, out-of-hours GP services and walk-in centre facilities in Greater London. It will secure contracts from emergency care practitioners in order to pay back the Futurebuilders investment and become self-sustaining.
The £399,000 package is made up of a £300,000 capital grant, a £34,000 revenue grant, a £25,000 capacity building grant, a £10,000 development grant and a £30,000 overdraft guarantee.
"If you lend money to start-up third sector organisations, it will show as a huge debt on your balance sheet, and that is not a strong financial position from which to win contracts," said Richard Gutch, chief executive of Futurebuilders.
"Quasi-equity is a good method because we get a good return on the investment, which is linked to the royalties on an organisation's contracts. If the group does well, we get a higher return than we would with a traditional loan."
Gutch said Urgent Care was a good prospect because it was applying for contracts from a large number of PCTs in London. But he said the quasi-equity approach would not be appropriate for organisations chasing one particular contract for a very specialised service.
Bamber Postance, chief executive of Urgent Care, said: "This new form of investment gives us the backing and flexibility we need to help us roll out our services across London."