The Pennines restricted canal development, so the railway provided a realistic alternative, especially with the growth in coal usage from the mines in the North East and Yorkshire.

In addition, steep gradients were to be avoided as they would require more powerful locomotives, while since speeds were expected to be less than about 30 mph, curves were considered less of a problem.

Although the government was in favour of the development of trunk railways to stimulate economic recovery and to facilitate the movement of troops in times of potential civil unrest, it was legally necessary that each line be authorised by a separate Act of Parliament.

While there were entrepreneurs with the vision of an intercity network of lines, such as those through the East Midlands, it was much easier to find investors to back shorter stretches that were clearly defined in purpose, where rapid returns on investment could be predicted.

The boom years were 1836 and 1845–1847, when Parliament authorized 8,000 miles of lines at a projected cost of £200 million, which was about the same value as the country's annual gross domestic product (GDP) at that time.

A new railway needed an Act of Parliament, which typically cost over £200,000 (about $1 million) to obtain, but opposition could effectively prevent its construction.

The railways largely had exclusive territory, but given the compact size of Britain, this meant that two or more competing lines could connect major cities.

[3] All the railways were promoted by commercial interests; as those opened by the year 1836 were paying good dividends, financiers wanted to invest in them, and by 1845 over a thousand projected schemes had been put forward.

Unlike most stock market bubbles, there was a net tangible result from all the investment in the form of a vast expansion of the British railway system, though perhaps at an inflated cost.

The best example of this is London, which has no fewer than twelve main line terminal stations serving its dense and complex suburban network, the result of the many railway companies that were competing during the Mania to run their routes in the capital.

[4] While it had been necessary to obtain an act of Parliament to build a new railway, the government initially took a laissez faire approach to their construction and operation.

The first investigation was conducted by Colonel Frederic Smith into five deaths caused by a large casting falling from a moving train in 1840 (Howden rail crash).

[7]Some opponents in 1835 saw the passing of a glorious era: We denounce the mania as destructive of the country in a thousand particulars – the whole face of the Kingdom is to be tattooed with these odious deformities – huge mounds are to intersect our beautiful valleys; the noise and stench of locomotive steam-engines are to disturb the quietude of the peasant, the farmer and the gentleman....Railroads will in their efforts to gain ground do incalculable mischief.

When Bristol businessmen wished to build their railway linking their city with London, they chose Isambard Kingdom Brunel as their engineer.

[10] By the 1850s, many steam-powered railways had reached the fringes of built-up London (which was much smaller than now),[vague] but the new lines were not permitted to demolish enough property to penetrate the City or the West End.

Towards the end of the 19th century, competition became fierce between companies on the east and west coast routes to Scotland, leading to the "Race to the North".

A brief note about each of the larger companies will illustrate how they grew to the importance they had assumed by the time of the huge amalgamations which took place in 1923, in which all but a very few railways were absorbed.