​The Boston and District Angling Association have within their constitution the following rules-

A LANDING NET, UNHOOKING MAT, AND A RECOGNISED METHOD OF UNHOOKING FISH  MUST BE AVAILABLE FOR USE WHEN PREDATOR FISHING ON ANY OF THE ASSOCIATIONS WATERS

ALL FISH  MUST BE RETURNED ALIVE TO THE WATER THEY WERE CAUGHT FROM (This rule supersedes the national by-law regarding the removal of fish regardless of size)

Therefore  ANYONE removing fish from Boston and District Angling Association waters is committing an offence under the Theft Act 1968.  The Association is actively involved in the promotion and support of The Angling Trusts Operation Traverse to combat fish theft and illegal fishing.

Here is a handy flowchart which has been jointly produced by Lincolnshire Poilice, The Environment Agency, and the Angling Trust. Hopefully it will help clear up the uncertainty about how to report suspected illegal fishing in the Boston area.