The first ever main line railway came into operation between Stockton and Darlington in 1825. The first conveyance of mail by railway took place on 11 November 1830, on the Liverpool and Manchester Railway, less than two months after the opening of this second main line (see 11/52).
The Post Office soon realised the potential for major improvements in mail distribution offered by this new form of transport. The first experimental Travelling Post Office, then known as 'the railway post office', ran between Birmingham and Warrington in January 1838 on the Grand Junction Railway. It consisted of a horse box converted into a primitive sorting carriage, coupled to a train. The experiment proved that mail sorting could be carried out efficiently on board trains, saving both time and money. In April 1838 a regular service started on the newly opened London and Birmingham Railway, with purpose built sorting carriages. By the end of the year through services had been established between London and Preston. Thereafter the TPO network grew rapidly, accelerated by introduction of the Penny Post in 1840, proliferation of new rail routes and railway companies in the 1840s, the increased volume of mail in circulation and general economic expansion. Railway mail services quickly swallowed up the role of the mail coaches. Previously, some sorting of mail was done by mail coach staff and postmasters at coaching inns. However, TPOs enabled large quantities of mail to be sorted and processed on the move.
Despite the rapid expansion of TPOs, the department in charge was known as the Mail Coach Office until 1854. The 1850s and 1860s saw further expansion and by 1867 the TPOs had their own Department at GPO Headquarters in London, headed by a Surveyor of Travelling Post Offices.
Overall management of railway services resided in the Inspector General of Mails. Control of TPOs remained based in London which was the focal point of much postal traffic. In 1882 the London Postal Service was created. The post of Chief Superintendent, TPO Section, was established one year later. During the 19th century the Post Office developed an intricate and comprehensive network of Day and Night services covering England, Wales, Scotland and Ireland. The Act to Provide for the Conveyance of Mails by Railways, 1838, allowed the Postmaster General to compel railway companies, for reasonable remuneration, to carry mails by ordinary or special trains, at such hours as the Postmaster General might direct, together with mail guards and other officers of the Post Office. Companies could also be required to provide carriages fitted up for sorting letters en route. This Act provided the foundation for all future arrangements with private railway companies and British Rail for carrying mails by rail. The first railway mail services were normally carriages attached to passenger services, which provided accommodation for sorting and / or conveying mails. By the mid-1860s a number of special trains run purely for postal requirements with very little or no passenger accommodation, were in operation as part of mail carrying contracts agreed between railway companies and the Post Office. In 1885 special mails, exclusively for Post Office use, were introduced between London Euston and Aberdeen. Known as the Up Special TPO and Down Special, they constituted a major reorganisation of the West Coast route, greatly accelerated TPO services to Scotland and formed the biggest and busiest of the TPOs.
In the years leading up to the First World War there were over 130 TPOs in operation throughout the United Kingdom, ranging from the large and prestigious London based services, such as the North Western TPO and Great Western TPO, to small local links, such as the Grimsby and Lincoln Sorting Tender and Brighton and Hastings Sorting Carriage (see 18/11-12). After the First World War, 1914-1918, many TPOs and Sorting Carriages which had ceased operating during conflict were not restored (see 18/38 for comparison of 1914 and 1922 service lists). Day TPOs and parcel sorting on TPOs were particularly reduced. The slow economic recovery during the 1920s delayed substantial re-investment in TPO rolling stock until the 1930s. During the Second World War all letter sorting on trains ceased and only a few key bag tenders ran. Parcel sorting and day-time TPOs were radically reduced after the War, mainly because the number and frequency of collections and deliveries had been reduced by concentration of processing services. A phased reinstatement began in 1945, but only about 46 services were restored. In 1948 the railways were nationalised and the British Transport Commission, (replaced by the British Railways Board in 1962), took over the TPO contract with Post Office. There was little change to the system from 1950 until 1968, when the Two-Tier letter service was introduced and TPOs began to carry and sort only First Class mails for next day delivery. The resultant drop in overnight business led to the disappearance of some services during the 1970s, including the Plymouth-Bristol and Crewe-Bangor TPOs. The overall size and shape of the network remained largely unchanged until the mid-1980s. Concentration and mechanisation of letter mail handling in addition to faster British Rail services and greater use of road and air facilities, led to a review of East Coast services in 1985, and in 1988 the first major revision since the Second World War occurred. A new timetable was issued for a system of 37 TPOs, some services were combined, others extended and new ones added including services such as the Manchester-Dover TPO, which by-passed London (see 18/68). Further large scale revisions and alterations took place in the 1990s to fit in with Royal Mail policies (see 18/66-67). By 1994 there was a limited provision of 24 TPOs. However, these were larger and faster trains, operating only at night and using specialised railway rolling stock.