[5] In its 21 years of operation, it also served as a station for royalty; in the short period when the Dowager Queen Adelaide was resident at Cassiobury House (c.1846-49), this station was remodelled to provide her with a royal waiting room, and it was also reportedly used by Queen Victoria and Prince Albert on a trip to visit Sir Robert Peel in November 1843, when they travelled by road from Windsor Castle to take a train from Watford to Tamworth.

The Grade-II-listed Old Station House still stands at 147A St Albans Road, a rare surviving example of architecture from the beginning of the railway age; today, the building is occupied by a second-hand car dealership.

Now mostly closed, this route began by running south and west to a more central station on Watford's High Street, which remains in use.

From 1846, the L&BR was absorbed into the London and North Western Railway (LNWR) and Watford Junction was now run by this large, ambitious company.

A second suburban branch line was also built from High Street west towards Croxley Green to serve new housing developments in that area.

Southern operated an hourly service from Milton Keynes, now starting from Watford Junction, to East Croydon with connections to Brighton and Gatwick.

[10][11][12] The expression reflects the station's position as the last urban stop on the main railway line out of London to the north of England.

In more recent years, it has been suggested that the phrase references Watford Gap services on the M1,[13] however the original saying was in existence well before its opening in 1959.

They may be delayed because the redevelopment of Watford Junction has been placed within the pre-qualification pool of proposed schemes by the Department for Transport.

[20] On 23 January 1975, an express train from Manchester to Euston derailed just south of Watford Junction after striking some stillages that had fallen on to the track.

The stillages had fallen from a Ford company goods train that had passed the station a few minutes earlier, conveying car parts from Dagenham to Halewood.

The RAIB investigated the incident, and concluded that the lineside cabinet door had not been properly secured during maintenance work the previous night.

The investigation also noted that the maintenance crew were likely suffering from fatigue due to a pattern of consistent night-shift work, regular overtime, and short-term sleep deprivation.

[22] On 16 September 2016, Class 350 electric multiple unit 350 264 collided with a landslide, caused by heavy rain the previous night, at the entrance of the Watford Tunnel and derailed.

[25] Watford Junction is also served in both directions by the Lowland Caledonian Sleeper service between London Euston, Edinburgh Waverley and Glasgow Central which runs on Sunday-Friday nights.

[27] Platform Usage: (Platform 5 was used by the Bakerloo line services of the London Underground until 1982, and removed as part of the subsequent major rebuild) Local buses run to destinations including Heathrow Airport, Stanmore, Uxbridge and Brent Cross in London, Amersham, Chesham and High Wycombe in Buckinghamshire, Hatfield, Harpenden and Hertford in Hertfordshire, Luton Airport in Bedfordshire and Harlow in Essex.

Studio Tour London – The Making of Harry Potter shuttle bus route 311 also leaves from the station forecourt.

[32] Assuming the ongoing increase in demand on the orbital route between Watford Junction and the West London Line, a significant increase of peak capacity services is needed, as the current service forms the only link between the Watford Junction and Kensington Olympia corridors.

This proposal suggests increasing West London Line – Watford Junction/Milton Keynes Central peak service to three tph and increasing present off peak services from an hour to every 30 minutes as well as suggesting extending Southern trains from 4 car to 8 car to help ease overcrowding further.

[33] The report recommends the addition of a tunnel in the vicinity of a proposed station at Old Oak Common connecting the Crossrail route to the West Coast Main line.

This proposal has not been officially confirmed or funded, although an announcement made in August 2014 by the transport secretary Patrick McLoughlin indicated that the government was actively evaluating the possibility of extending Crossrail as far as Tring and Milton Keynes Central.