The opening of the Olympic Games and the summer holiday getaway could create "the perfect traffic storm", a roads' information company said today.

Londoners will face increased traffic congestion of 33% during the Games, predicted the Inrix company.

Traffic on main routes will slow to just 12mph in late July and early August.

It said the first three days of the Olympics posed the greatest risk of traffic troubles.

But Transport for London (TfL) dismissed Inrix's findings as "without foundation" and said they were based on "false assumptions" and "incorrect, out of date information".

Inrix said the Olympic opening ceremony on Friday, July 27 clashes with one of the busiest holiday getaway weekends of the summer when traffic levels are already around 30% above average.

This event is followed in quick succession by the men's road cycling event, which will "close thousands of roads throughout south-west London and Surrey".

Inrix said a trial event for the race in August 2011 "resulted in traffic chaos, when journeys of just a few miles took several hours and some drivers were forced to abandon their cars".

Inrix traffic analyst Greg Hallsworth said: "Traditionally, the weekend of July 27-29 is one of the busiest holiday getaway weekends of the year.

"Combine this with the Olympic opening ceremony and the road cycling race and we could have the perfect traffic storm."

Garrett Emmerson, chief operating officer for surface transport at TfL, said: "TfL has spent the last six years planning for the Games. The traffic flow, vehicle trips, congestion hotspots and journey times data we've collected has helped us build an accurate picture of what the impact will be on London's streets during Games time, which we have already published on our website.

"As a result, we know that 70% of journeys on London's roads will be unaffected by the Games, and we have been working closely with businesses and the freight industry for the last year to help reduce the number of non-essential journeys made on the remaining 30% of the road network."