The Hexham and Allendale Railway was a railway company formed in 1865 to build a branch line from the lead mining district of Allendale in Northumberland to a junction near Hexham on the Carlisle to Newcastle line. It opened to goods and mineral traffic in two stages from 1867, and to passengers in 1869.
The area was thinly populated apart from the lead mining and smelting settlements, and a slump in lead prices around the time of opening made the financial status of the line difficult, and it was not completed to its intended southern terminus of Allenheads.
The company was absorbed by the North Eastern Railway in 1876, and the passenger service was withdrawn in 1930; the line closed completely in 1950.
The Newcastle and Carlisle Railway was built to connect the east and west coasts of northern England, but in its construction, priority was given to opening the section between Hexham and Blaydon. This was to give early access to the River Tyne for lead ore extracted in the area, considered to be the most lucrative potential traffic for the line. The Newcastle and Carlisle Railway was completed (from Carlisle to Gateshead) in 1837.
Much of the ore was extracted from hilly locations north and south of the N&CR main line, and for some time it was carted down to the N&CR at Hexham or Haydon Bridge for onward conveyance by train. This was an improvement on the previous arrangement, but it was not long before proposals for railway connections were put forward. As early as 1841 the Newcastle and Carlisle Railway considered a connection to Alston and Nenthead, high in the hills south of and above Haltwhistle. The Nenthead part of that was dropped, but the branch line from Alston to Haltwhistle was opened in two stages in 1851 and 1852.
A rival proposal to the N&CR Alston branch had been the Wear Valley Extension Railway, which was proposed in 1845 to build from Frosterley on the Wear Valley Railway to near Milton on the Newcastle and Carlisle Railway main line. Sponsored by the this was conceived as part of a future through main line route to Scotland. The terrain was very challenging, and attempts to keep to main line curvatures and gradients had to compromise with realistic earthworks. Opposition from the Earl of Carlisle, the major landowner in the area, resulted in the proposal being dropped in 1846.
Now in the same year the Newcastle and Carlisle published their intention to build a branch to Allendale from Morralee, but they were unable to prepare timely and accurate survey documents for the line through difficult terrain and the plan was deferred; even the Alston branch, serving a greater concentration of the lead industry, was much delayed in opening..