You are slightly vague in which aspects of Environmental legislation you wish to address, this is a vast field of compliance and legislation.
Obviously providing evidence that you are complying with the WEEE directive is a start, if you are disposing of any waste then there should be a waste transfer note produced for each movement detailing the type, quantity start and destination of the waste, probably prepared by the registered waste carrier removing it, if it is hazardous waste then there should be a consignment note with full hazard, consignor, waste type, consginee details.
In terms of environmental pollution then you should have procedures in place detailing how hazardous materials are handled and how they are controlled to prevent release into the environment, whether that be by air, land or water. COSHH assessments should be in place for all hazardous materials used.
Risk assessments should also cover a lot of this information.
If the levels of hazard are great then there should be emergency plans in place under COMAH, probably not applicable for an electrical installation business.
General waste collections would be detailed in your invoices from the waste company (and should also have something like an annual waste transfer note for the collection round)
This is all I can think of immediately and is mainly concerned with waste management as this is what I know, there may be a whole range of other areas at which you should be looking but this would be a good start.
