As you are now gathering, burying it was not your best idea. Many local authorities will allow non-commercial disposable asbestos free of charge.
Asbestos is Hazardous Waste within the provisions of the Hazardous Waste Regulations 2005.
If this was private you are also bound by the Control of Asbestos Regulations 201 and section 33.1 point see of the Environmental Protection Act 1990 disposal of controlled waste in a manner likely to cause pollution to the environment or harm to human health.
There is a whole raft of legislation covering asbestos.
What penalty are you likely to get? Potentially, community service, and a fine which could be up to a couple of thousand pounds.
Thank you for letting me assist you with your legal question. I am glad that I was able to help.
I am not certain whether that answers the question for you or not, but I am happy to answer any specific points arising from this.
It will be my pleasure to help you again either further with this or any future questions you have