West of Brockenhurst, it ran via Ringwood; at that time Bournemouth was not considered an important settlement and Poole was served by a branch to Lower Hamworthy, across a toll bridge from the town.

Proposals were put forward as early as 1836,[4] but it was not until 1847 that the company connected Salisbury in to its network, and that was a branch from Bishopstoke (Eastleigh), giving a circuitous route from London.

Before that, in 1844, Charles Castleman, a solicitor prominent in Wimborne Minster, had independently proposed a westward line from Southampton via Ringwood to Dorchester, and possibly on via Bridport to Exeter from there.

[3] He presented his report on 18 July 1844; his line would leave Southampton and run through Brockenhurst, Ringwood and Wimborne, then turning south to Poole and west again to Wareham and Dorchester.

Interests in Weymouth were dismayed that the line was to end (for the time being) in Dorchester; they were anticipating the loss of Channel Islands packet traffic (post and the transport of official documents by sea) to Southampton.

[3] Castleman realised that he needed the support of a larger company, and the LSWR was the obvious choice, as it would bring London traffic to them at Southampton, and enable them to extend to Exeter.

He approached the LSWR with the idea but was rebuffed; evidently they wished to concentrate on reaching Exeter through Salisbury, and they hinted at branches from such a line into Dorset.

Castleman now took the bold step of offering his line to the rival Great Western Railway, in a letter dated 30 July 1844.

Referring to the LSWR he said ... An act, however, of undoubted duplicity on their part, makes me fearful to trust them as they have a scheme of their own for supplying the County of Dorset by means of a line from Salisbury ...

[3] Castleman was encouraged now, and Moorsom quickly completed the necessary plans of the route; the GWR guaranteed a 3.5% dividend on S&DR shareholdings, and a bill was presented to Parliament for the 1845 session.

Castleman had given a personal undertaking that the route within Southampton would be on the foreshore, across the mudlands, and would probably have much improved trade in the lower town, but the LSWR were now in control.

However the Pier Commissioners demanded the use of horses, and not locomotives, throughout the quays at Southampton, and the LSWR refused to give any such undertaking, and decided upon an alternative route that ran on the landward side of the town and would require a tunnel.

[8] From Brockenhurst the line was to run westward through Ringwood and Wimborne, trending southwest through Broadstone and Wareham, and then west to Dorchester.

The support given to these schemes was in direct disregard of undertakings mutually given at Dalhousie's suggestion (see above), and the Southampton and Dorchester directors saw that their supposed protector was improperly sponsoring a line that would abstract from their own.

It was not until July 1846 that agreement was made; by then the contractor Morton Peto had completed the Ringwood to Dorchester section by the previous November.

The public opening was planned for 1 June,[9] but on 30 May the interior of the Southampton tunnel suffered further problems, with a large bulge in the walls indicating a section was sinking.

[7] With no connection to the mainline to London, the Blechynden terrace station was the terminus; the LSWR had to transport their locomotives there by road through the streets of Southampton.

It appears that Mr Peto the contractor, for the accommodation of those parties whose property lies above the line of the old Tunnel, agreed to strengthen it by building a certain number of cross walls at short intervals.

The mode adopted in doing it was to drive a small gallery laterally from the side of the new Tunnel to reach the old one at a point some distance beyond the 20 feet which had been solidly built up.

The section of line from Blechynden to the LSWR terminus only opened for traffic from the night of 5–6 August 1847, although there were passengers on a test train which ran on 29 July 1847.

[6] There was a serious collision on 20 September 1847, near Wool; the mail train from Dorchester was very late in reaching Wareham, and the stationmaster there sent a pilot engine out on the single line to find out what was wrong.

[3] In the short independent life of the Southampton and Dorchester Railway there was no change to the number of stations or their location, although Leonards Bridge may not have survived long.

[6][17] When the Southampton and Dorchester line had been conceived, Bournemouth was an insignificant hamlet surrounded by barren and hilly heathland, and there was no reason to make a railway connection.

The route was still circuitous, and was a branch off the main line, so that many express passenger trains divided at Brockenhurst, with separate portions for Weymouth via Wimborne and Bournemouth via Christchurch.

Freight traffic continued to Ringwood until August 1967 before being truncated yet again, this time back to a military fuel dump at West Moors.

Present-day passenger trains between London and Weymouth run from Lymington Junction via Christchurch and Bournemouth on the South West Main Line.

The mileposts along the surviving portions of the Southampton & Dorchester Railway west of Hamworthy Junction are measured from London Waterloo via the direct route through Sway, Bournemouth and Poole.

It looked into the feasibility of reopening disused lines and stations, and concluded that there was a business case for investing £70m in the new link with an hourly service.