A report recently arrived on the Wireless Waffle newsdesk of the discovery of some kind of (probably illegal) transmitter discovered on land in Surrey next to a military establishment. According to the report:

Army bomb disposal experts were called to Camberley on Monday morning to deal with a "suspicious" object that turned out to be a radio device... Shortly before 3pm, Surrey Police said the unit had been confirmed to be a "transmitter or repeater for a citizen or pirate band radio station", and that roads had been reopened and cordons lifted.

Of course this piqued the interest of the Wireless Waffle team. Let's look at the possible options:

CB Repeater
Such things do exist but require a great deal of technical skill to install and operate. As CB radio operates at 27 MHz, they generally require large antennas, and as transmitter powers are usually at least 4 Watts, need power supplies the kind of size that wouldn't easily be left lying around in a piece of woodland.
Probability rating: ***** (2 out of 5)

Pirate Repeater
Not something that is often heard of, in fact, do a 'google' search and nothing of any substance comes up. One possibility is that it could have been a PMR446 repeater which, whilst not strictly legal, is not fully pirate as it operates on an unlicensed basis. Such devices would (sensibly) be located on high ground, though they could be operated from batteries for some time. Ideally, they would be high off the ground too (the news report does not indicate whether the so-called repeater was on the floor or up a tree).
Probability rating: ***** (1 out of 5)

FM Pirate Transmitter
Most FM pirate stations in the UK use transmitters on top of tower-blocks. The area in question is clearly not one bedecked with such skyscrapers, it is woodland. It is not unheard of for pirates to put transmitters up trees but there are better places, especially those with power and somewhere dry to put the transmitter. There aren't that many pirates in this area, Point Blank FM was one which used to broadcast specifically to the area but it hasn't been on air in that part of the world for many months. Pressure FM (also known as 'Presha') is another station in that part of the world. It is possible they would use a site such as that, but if they were locals, presumably they would know the area was largely military and steer clear of it?
Probability rating: ***** (4 out of 5)

Short-Wave Pirate Transmitter
Short-wave pirates are almost uniquely confined to woodlands in order to string up the large antennas necessary given the frequencies they use. They often use hidden battery powered equipment. On the face of it then, this is exactly the kind of place you would expect to find such a transmitter. The bigger question is whether any such pirates operate from that part of the country, the answer to which is, of course, 'who knows?' Certainly there is some history in the area including Radio Fax which used to operate from Surrey in the late 1980s, and of course, the infamous Radio Jackie which used to operate from the London end of Surrey. There's also a vague recollection of a maildrop for short-wave pirates that was in that part of the world (though my memory is a bit hazy on that). Anyhow, it's not impossible but the number of UK-based short-wave pirates seems very much in decline.
Probability rating: **** (3 out of 5)

Our conclusion then - probably an FM pirate - but a bit of a stupid one to go so near to ministry of defence land!