The firm, which also helps run the London congestion charge, expects to make £15m this
year, on revenues of around £155m.
Senior management, led by chief executive Mark Underwood, will reinvest in the
business and Underwood said he saw “significant opportunity to expand the business
over the next few years”.
NSL branched out into ambulance services by buying Patient First earlier this year, and is part of a scheme to bring regulated parking to Abu Dhabi.
The firm provides more than 50 local authorities with private parking enforcement officers.
It was previously part of NCP, the car parks business, which 3i bought in 2005. The private equity firm then split the two and sold NCP to Australian bank Macquarie.
Taken together, the two sales will yield a return to 3i of about three times the money it originally invested, a person familiar with the matter said.