Delays due to congestion in the UK’s most gridlocked cities has risen 20% since 2010, with journeys now taking almost a third longer in peak times than in free-flowing conditions, according to new data from TomTom.

City-based drivers are losing an average of 16 working days per year to traffic, according to TomTom.

The TomTom Traffic Index looked at conditions in the country’s busiest cities, finding that the difference between peak and off-peak journey times had reached 30% this year, up from 25% in 2010. This equates to 129 hours per year, or eight working days, lost to congestion.

It also results in substantial costs due to lost productivity. Based on a driver earning minimum wage, and the van parc in those cities, TomTom estimates the UK is wasting £915m per year having employees sat in congestion – up from £767m last year. A quarter of that (£264m) is in London alone, where peak-time journeys can take 40% longer than travelling the same route off-peak.

Beverley Wise, director uk & ireland for TomTom Telematics, said it’s never been more important to plan routes to avoid peak traffic: “Although solutions to the wider traffic problem are incredibly complex, businesses can take action now to mitigate its effect by using data to develop smarter working schedules and shift patterns that help employees avoid driving at peak times.

“Technology such as telematics can help in the move towards a more dynamic model of routing and scheduling that uses data on traffic and journey times to develop plans that minimise time on the road and can be quickly adapted in reaction to delays or changing circumstances.”