I have queried the accuracy of this information due to the name Westcliff on sea not appearing until the early 20th century. From an 1880 Ordnance survey map, surveyed in 1873 the terminus at Southend was in an area known as Clifftown. Westcliff station location (built 1895) was south of Hamlet House on this copy of said map:
https://maps.nls.uk/view/102342026# As you can see, at that time there were no buildings in the area to suggest the need for a station at such a location (except perhaps a landowners halt), and there is no mention on the map of Westcliff at all. There was supposed to be an 1893 map but I have yet to locate a copy. Zooming in on the map you can see the actual track layout of the terminus in 1873. Clearly there must have been a huge building boom in the 1880s to justify not only another station at Westcliff but also the GER branch from Shenfield to Southend, opened 1888-9, with an additional station at Prittlewell, where some of my ancestors lived. Unfortunately the libraries where I live do not contain many English books and none about railways and although I have a large collection on GER books I have next to nothing on the LTSR.
1895 map but nothing west of Clifftown:
https://maps.nls.uk/view/101456087
1895 map showing Leigh to Clifftown:
http://www.oldmapsonline.org/map/nls/101456084 town shown simply as Westcliff and station as Westcliff also (no mention of 'on sea'). Any photos of the opening day showing a legible nameboard? Clearly Southend has expanded and been renamed Southend on Sea and the new Westcliff station is at the western extremity but perhaps further expansion is envisaged or the railway is enticing Londoners to visit previously less accessible beaches!
Here is another map from a survey in 1920-23:
https://maps.nls.uk/view/101457413 another good layout diagram for Southend station.
Related to this my father apparently worked on the railways for a short time in 1920s or 30s, involved with overnight Fish trains from Southampton to London, so my sister told me yesterday! More on that later. Was there ever a rail link to Billingsgate Fish Market?