Fly-tipping is the illegal dumping of waste and this can be reported to your local council.
Large scale illegal dumping (such as lorries dumping rubbish) and hazardous waste can be reported to CrimeStoppers
If the rubbish is on private land it is the landowner's responsibility to remove it. The council can come and remove it but this may incur a charge.
If the rubbish is on council land you should contact your local authority to come and remove it.
You should not try and remove the rubbish yourself if you do not know what substance has been disposed of as it may be harmful.
See the websites in Related Information to find your local authority's contact information.