It's must be a misprint - it's West.
For Longitude, the first three digits are degrees East or West of the prime meridian, next two are minutes (60 minutes = 1 degree) and the last two are seconds (60 seconds = 1 minute).
So Shoreham is 0 degrees, 17 minutes and 57 seconds West of the Prime meridian.
With Latitude there are only two digits, as you can be a maximum of 90 degrees away from the equator. Hence Shoreham is 50 degrees, 50 minutes and 3 seconds North.
On the half-mil charts there are lines of longitude and lattitude marked every 30 minutes.