Almost half of the network has been rated ‘poor’ in a review to be published on Monday

It spans 16,505 miles, is seven times longer than our motorway system and carries half as many people each year as the UK’s creaking railways – all for free and with no carbon emissions. But the National Cycle Network is so starved of funding that many of its bike paths are “crap” and desperately need improvements, according to the charity responsible for its development and upkeep.

The network, marked by blue and red signs, includes 5,273 miles of traffic-free cycle paths, bridleways and canal towpaths used by millions of cyclists and walkers each year. It also incorporates 11,302 miles of “on-road” sections, covering the length and breadth of the UK from the Shetland Islands to Land’s End and from East Anglia to the Giant’s Causeway in Northern Ireland.

A review to be published on Monday by Sustrans, which has built the network over the last 23 years, reveals that 42% of it has been rated as “poor” and a further 4% “very poor”. Large sections fail to fulfil one of its key aims: that it can be used “by a sensible 12-year-old travelling alone”.

Xavier Brice, Sustrans chief executive, told the Sunday Times: “We’ve had enough of the crap bits and want to make it fit for everyone.”

There are 15,680 incorrect, missing, obstructed or confusing signs on the network and 16,435 barriers, including steps, bollards and gates, according to the review.

Other complaints include sections that turn into a “mud bath” each winter, slippery cattle grids and even the odd ford.

About 24% (2,596 miles) of the on-road sections are too fast for safe cycling and could be candidates for speed limit reduction schemes, Sustrans argues. It wants the speed limit on rural roads used by the Network reduced to 40mph and urban roads to 20mph as it plans a further 5,000 traffic-free miles in the next 22 years.

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Despite its name, the network is popular with walkers, joggers, wheelchair users and horse riders as well as people on bikes. More than half of the UK population lives within a mile of their nearest route and 4.4 million people used the Network last year, making 786m trips.

Facebook Twitter Pinterest Looking south at cyclists on Drake’s Trail National Cycle Network Route 27 in Devon. Photograph: Alec Scaresbrook/Alamy

Sustrans says it would cost £2.8bn to improve and expand the network. “This is a small amount compared to what we spend on the road network in the UK, and the return on investment is many times higher,” its review argues.

Each year, the network saves the UK economy nearly £90m through reduced road congestion, according to Sustrans. Its health benefits save the NHS the equivalent of 2,206 nurses’ salaries, and leisure and tourist trips contribute £2.5bn to local economies, the charity claims.

In his recent budget, the chancellor, Philip Hammond, pledged £30bn for road improvements targeted primarily at motorists.

“Politicians across the UK are grappling with problems like congested roads, air pollution and increasing levels of obesity. In pure transport terms, the National Cycle Network presents a huge opportunity to transform the way people travel. But the benefits of investing in the network can be seen right across government like relieving pressure on the NHS budget,” said Brice.

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Sustrans receives £9m a year from the Scottish government to fund the network in Scotland but no guaranteed regular funding from the UK government for the English bits.

Jesse Norman, the government’s cycling and walking minister, said: “This report shows that more needs to be done to make [the network] fully accessible, and that’s why earlier this year the government dedicated £1m to support initial work repairing and upgrading sections of this popular network.”

‘I won’t ride the off-road sections alone’

My 11-mile cycle commute from Stockport to central Manchester uses two off-road sections of the National Cycle Network. In the summer, they are my favourite bits of the ride, taking in Reddish Vale country park – which includes a river, duckpond and splendid 17-arch viaduct – and the Fallowfield Loop, an old railway line that is a blackberry pickers’ paradise in early autumn. The problem is that neither are lit, so I won’t ride them alone to and from work in winter.

Then there are the niggles. Route 62, which is part of the Trans Pennine Trail, idiotically directs cyclists down some steps in Reddish Vale. It also includes a number of access control gates, which are too narrow for mountain bike handlebars, and a few annoying horse stiles, which mean you have to get off and carry your bike across two wooden steps.

I then join Route 6, which starts all the way down in London and will reach Threkeld in Cumbria when it’s finished. I only do four miles of it, however, to reach the student district of Fallowfield in south Manchester. There is a lot to love about the Fallowfield Loop: it’s almost flat, has a nice smooth surface and most of the barriers have been taken out. But it has been plagued by muggers in recent months. At least one female cyclist has had her bike stolen at knifepoint, deterring many others and forcing me back on to Manchester’s polluted streets.

NCN problems

NCN 5, the North Wales coastal route from Chester to Flint

Problem: Current route sends users along a very busy and fast section of A-road between Flint Castle/railway station and Connah’s Quay.

NCN 76, Manor Powis roundabout, Scotland

Problem: Path users exit from a traffic-free section directly on to a very busy multi-lane roundabout on the A907, east of Stirling. The roundabout is a key barrier for users of the well-known Round the Forth circuit, heading to and from Clackmannanshire.

NCN 94, bridging the River Bannfoot, Northern Ireland

Problem: The 113-mile Lap the Lough circuit of Lough Neagh, the largest freshwater lake in Britain and Ireland, is very popular with day-trippers and people who enjoy cycle touring, but this unbridged river requires a very circuitous diversion away from the Lough shore down to, and through, Portadown.

NCN 4, barriers on the Kennet and Avon cycle route in Reading, Berkshire

Problem: Four restrictive, awkward barriers within two miles make access very difficult to this otherwise good and very popular riverside route, which forms a central part of the high-profile EuroVelo Route 2.