Complex sentence: British Transport Police opened an investigation into the events before the accident, which will centre on whether or not Anglian Water gave proper training to visitors to the sewage works in relation to the correct use of the level crossing.
Split into simpler sentences: British Transport Police opened an investigation into the events before the accident. The investigation will centre on whether or not Anglian Water gave proper training to visitors to the sewage works in relation to the correct use of the level crossing.