What's 40 years old and worth £2.1bn?

It is 40 years old, has thousands of careless users every day, and is so broken in parts that it is under constant repair. But, according to government accountants, the M1 motorway is now officially worth £2.1bn - more than 40 times what it cost to build.

It is 40 years old, has thousands of careless users every day, and is so broken in parts that it is under constant repair. But, according to government accountants, the M1 motorway is now officially worth £2.1bn - more than 40 times what it cost to build.

The valuation of the road, which runs 187 miles from London to Leeds, has been carried out as part of an assessment of the value of all national assets.Departments have been asked to present their prized possessions and heirlooms - both ancient and modern - for valuation by in-house experts.

When it came to the M1, officials at the Department of the Environment, Transport and the Regions were asked to assess not what it would fetch at auction, or its insurance value, but what it would cost to replace. Their answer, considering its provenance (attributed to the notorious transport minister Ernest Marples) and chequered history (sundry gangsters are said to adorn its bridges' interiors), was £11.3m a mile.

The news will come as a surprise not only to the road's cone arrangers, maintenance gangs and greasy bacon sandwich servers, but also to the 88,000 users who daily brave its delays and varied surface.

The Highways Agency, which owns the motorway and trunk road network, said its accountants had had to "break new ground" in valuing its estate. Their £2.1bn price tag includes not only the cost of rebuilding the road, but also the value of the land and the cost of bridges and sliproads, and was adjusted to take its present condition into account. The road, which opened in November 1959, cost £50m to build.

One Highways Agency accountant said: "We had to establish a lot of principles, together with the Treasury, the National Audit Office and GAAP [generally accepted accounting practice] because we were breaking new ground. Some of these roads were built in Roman times." A Treasury official added: "No one had ever tried to value a road before."