If you’re looking for a way to boost your stress levels and set your blood pressure soaring, try joining the M25 at junction 21 at 5pm on a Friday afternoon. The northern section of the motorway between junctions 21 (the M1) and 31 (A13) is now the most congested stretch of road in the country, according to new figures released by Trafficmaster, a traffic monitoring company based in Cranfield, Bedfordshire. The busiest time is between 4pm and 8pm on Fridays and between 7.30am and 9am on Mondays.

Last year British motorists wasted an estimated 182m working days sitting in jams. And with traffic predicted to grow 33-40% by the end of the decade and up to 70% by 2025, according to government forecasts, the tailbacks can only get longer. The average motorway speed during the evening rush hour fell from 64.5mph in 1995 to 57.9mph in 2003 (the most recent figure available) and the cost to the economy is estimated to be between £15 billion and £20 billion a year.

Junction 21 of the M25 may be the most congested spot in Britain, but there are some close runners-up — the M6 between Stoke-on-Trent (J15) and Wigan (J26); the western section of the M25 between junctions 10 and 21; and the M1 through the home counties from junction 6A to junction 15. The most congested A road in Britain is the A14 between Huntingdon and Cambridge.

Other hotspots are along the M4 between London and Bristol, on the M5 between junctions 18 and 20, the M1 around Nottingham and Derby, the M62 in West Yorkshire, the A1M in Yorkshire and the M42 and M6 around Birmingham. The M8 through Glasgow is Scotland’s most congested road, according to Trafficmaster.

So what is being done to cut the growing cost — in money, time and frustration — of Britain’s congestion? Not enough, clearly. Earlier this year the Highways Agency, the government body responsible for monitoring and maintaining England’s motorways and major trunk roads, was criticised for being “timid and ineffective” and for failing to tackle congestion. The report, by the Commons public accounts committee, said the agency was hampered by excessive “bureaucracy and risk aversion” and showed a “lack of leadership, urgency and imagination”.

Motorists repeatedly complain of waiting in traffic alongside lines of orange cones, looking for workmen who have mysteriously vanished to finish other, seemingly never-ending roadworks.

The Sunday Times canvassed opinion at motorway service stations between Reading and Bristol and found drivers infuriated by a lack of information and incomprehensible working practices. “There are too many short stretches of roadworks on the M4 that seem to have been going on for ages,” said one frustrated commuter. “Why don’t they channel more resources into getting one bit done quickly then move on to the next bit?” Others complained of “ridiculous” speed restrictions, maintained even when there is clearly nobody at work, and of absent workmen: “I was on the M4 at 4.15pm on a clear, mild Friday afternoon. Guess what? The workmen appeared to have knocked off early in spite of the conditions being perfect for making faster progress.”

Why, ask many worn-out commuters, can’t the UK move towards a US model where teams of workmen, known as road gangs, close the roads only after midnight and reopen them before the following morning’s rush hour? The Highways Agency claims an increasing amount of work is taking place at night — about 55-60% according to its latest calculations, although “night” in the UK is defined as between 7pm and 7am.

“Every time a new set of roadworks are planned every attempt is made to cause as little disruption as possible to motorists,” said a spokesman for the agency. “That is always our top priority. Work is only carried out during the day where there is no alternative and usually the work is then continued around the clock.

“But preparation needs to be done before work can commence, so cones will often be in place before work gets under way and may stay in place to allow the surface to dry.” ()

The agency is not responsible for all of Britain’s roads. The Scottish parliament and Welsh assembly have responsibility for motorways and major trunk roads in their respective areas. All other roads outside London are handled by local authorities. In the capital Transport for London, the transport authority of mayor Ken Livingstone, handles the main thoroughfares while local boroughs are responsible for maintaining more minor roads.

Even when the Highways Agency is nominally in control the work is carried out by 14 outside contractors, each responsible for its own area of England. So it is hard to know how closely the agency can monitor working patterns around the country.

The sheer number of bodies involved in road maintenance and traffic management can also lead to clashes, with a series of roadworks springing up simultaneously along one popular commuter route. However, the agency claims to be addressing these issues. “Local authorities now have a ‘network management duty’ and have to look after the movement of traffic not just on their own network but also on adjacent networks,” said a spokesman. “From January this year they have had to appoint a traffic manager specifically to undertake this work.”