The ELF trust has some 1.1Km of river front and approx 10 acres of land designated as a Site of Special Scientific Interest that has regulations restricting activity thereon. It also affects any adjacent land that impacts upon it to some degree.
Link to the Act
Link to Regulations
Map of SSSI within ELF trust
Activities that are carried out.

Tresspassing:
Whereas trespassing, commonly, is a civil offence, damage is more likely to occur in an SSSI given it's delicate nature and so it is highly likely a liable offence will occur to the trespasser. This will include not just damage to the SSSI but where there are invasive plants an offence under the Regulations controlling spread of such plants as Japanese Knotweed.

ELF SSSI:
This site has numerous dangers
The marsh has numerous hidden drainage channels and sink holes, and is the surface to mine tunnels.
The riverside bund has subsided and there are areas where the high tide creates islands.
The site hosts invasive plants which are under management, but trespassing use can result in serious disturbance by spreading the invasive plants to new areas that are not known to the management team.