Present Spurn

The present peninsula started to form around 1600. In 1849 a storm breached Spurn (see strip12 on the map below) and "the peninsula became a string of islands" at high tide.
From the 1850’s onwards sea defences kept Spurn artificially in the same position. During the World wars it became a military stronghold - a reason to further upgrade the sea defences.
In 1961 the Ministry of Defence sold Spurn to the Yorkshire Wildlife Trust. The trust now runs the area as a nature reserve. The sea defences are left to deteriorate and the natural process can take over again. - Today erosion continues to eat into Spurn. At spring tide wash-overs of the neck occur from time to time.

(amended 21 July)

The map shows coastal changes around Spurn over the last 150 years. It combines 1st edition OS maps (1851/52) with recent aerial photographs (c Getmapping 2000).
Source: www.hull.ac.uk/erosion

I found this info in the following files:
Development of Spurn Peninsula
The Holderness Coastline - The Management of Coastal Erosion
SPURN HEAD by V.J. May

update 2019: all the original links as above (in small print) are no more active, but please see:
https://www.urbanrim.org.uk/cache/Pye&Blott_Holderness_Erosion.pdf