Firstly you are refering to a Lattitude and Longitude, that is not the same as a Grid Reference.
A Grid Reference is based upon a square graticule placed on a map or chart. i.e. National Grid. The scale is linear and decimal in nature. Measurements move away from the origin.
Lat and Long is not linear and is initially based upon Degrees and Minutes of arc. The minutes may then be sub-divided into seconds(base 60), or alternatively into decimal parts of a minute (base10). Unfortunately they are often presented in a manner where it is difficult to determine which system is being used. Unlike a Grid, Lat Long measurements may move in either direction hence E/W and N/S
Shoreham is as you say West not East.