The funders are: Bank of Scotland, ING Barings, First National, BMP Paribas, Bank of Tokyo and Co-operative Bank.
The service, called Maris Advance, will pay the capital cost of projects and then clients will reimburse the contractor at a fixed interest rate over three to five years.
Every part of a refurbishment project will be put under a single lease, from preliminary space audits and building surveys to installation of partitions, lighting, air-conditioning, furniture and floor coverings. Any upgrades or extra equipment could be added to the original lease.
Maris, a £60m-turnover firm based in London, is marketing the service to clients with projects worth between £500,000 and £14m. It is hoped the move to eliminate capital costs will stimulate demand for refurbishments.
Maris marketing manager Paul Sowerby said: "Equipment and office furniture leasing is well established but, until now, leasing fit-out projects hasn't been an option because banks haven't wanted to get involved.
"Banks have been very wary when approached about funding leasing deals for fit-out projects. Other fit-out firms offer a similar leaseback service without the financial backing – ours is the first to bring together so many banks to fund it."
Sowerby added that having six banks backing the scheme meant that the funding of larger projects would be divided up into smaller financial commitments, and could guarantee that a refurbishment scheme would receive funding.
Julian Smith, Maris' company secretary, is managing director of the venture.
Smith said that even after the set-up costs and interest charges, leasing a design-and-fit-out project could end up cheaper than up-front payment, as money that would have been spent on fit-out could be invested.
Lease payments are also 100% tax deductible; when a firm pays for a refurbishment after completion 70% is deductible.
Inspace, Willmott Dixon's fit-out arm, is piloting a similar service.