In the summer, it must be a very pleasant place indeed to pass the day. Families of military personnel do just that, enjoying picnics, sunbathing and paddling in the water. But members of the public don't have that option because the most of Thorney Island - including the beach - is closed to them for "security reasons".
I looked in vain for the barbed wire and radar sensors that would suggest the beach was top secret or worth defending. To the north I saw attractive woodland and vast fields of arable land that were, equally inexplicably, out of bounds. On the east side there is the RAF sailing club.
Thorney Island offers as strong a case for access as any for the Independent on Sunday's campaign to open up more MoD land to civilians. When training exercises are not taking place at Thorney it seems there is little case for the public to be kept at bay. But old habits appear to die hard: the MoD said there was never any military activity at the base - and denied there was a beach.
A map of Thorney Island is listed in a book of walks on MoD land but there is no indication of where you should start or pick up the path. Having found the path - through a shipbuilder's yard - we came to a fence monitored by closed circuit television where I had to give my name and address via an intercom system. Here stands the first signpost: this was MoD land, private property, guard dogs on patrol, so keep off.
Thorney Island is home to the Baker Barracks of the 47th regiment. But on the day we walked, we saw not a single soldier, tank or firearm. The Ramblers' Association believes keeping it off-limits is one of the most flagrant breaches of the MoD's privilege. "I walked along the path and found the sailing club with people sitting on the veranda in their uniforms sipping gin and tonics," said David Beskine, director of campaigns and policy at the Ramblers' Association. "All this area is off limits to the public because notionally there are training exercises going on. But it can't be top secret because if it was there would be fences stopping you from straying from the footpath. It is basically a private national park."
The MoD continues to insist there is no beach at Thorney Island. "These people live there; they have to have some land to exist on," said a spokeswoman for the MoD.Reuse content