London Borough of Wandsworth has extended its contract with supplier Liberata to collect business rates.
The original contract, worth £2.1m, was signed in 2010 and had been set to run out in 2017.
The council has now extended the deal for a further two years, but has refused to reveal how much taxpayer money will be spent.
Kevin Legg, assistant director of revenue services at the council, said: “We look forward to extending our partnership with Liberata.
“The results speak for themselves, as for the past three years the partnership has helped the council to achieve collection rates of 99%, placing it in the upper quartile for business rate collections across London boroughs.”
A previous version of the contract was signed in 1999 but expired in 2006, according to council documents.
The firm says it has collected £119m a year from almost 9,000 business in the borough. That amount is set to grow significantly as work continues on the Nine Elms regeneration scheme including new commercial development at the former Battersea Power Station.
Vijay Chandiramani, chief operating officer of local government business process services at Liberata, said: “In the face of ongoing challenges, it is important that councils ensure they can effectively collect due revenue.
“Our ongoing work with Wandsworth is a great example of how our sector specific expertise and effective process automation and data analytics is delivering a cost-effective, low-risk, and high-value services to local councils.”