I have a cable running through my garden which is 18ins" below the surface it supplies 93 houses should it be deeper and should it be running through the middle of my garden can any one answer my question in terms that I can understand? Many thanks Ali

You don't specifiy what 'kind' of cable this is: Electric? Cable TV? Telephone?

If it is electrical cable and the cable is in conduit, it is permitted to be run at an 18" minimum depth.

Otherwise, if it is not in conduit, it is required to be at least 24" deep.

Some electric utilities require service conductors to be at least 30" or more deep regardless of what electric codes say.

Should it be under your garden?

Yes, probably.

It is there by legal easement granted to your associated community or the municipality or the electric company or all 3.. And should not be disturbed under any circumstance.

You are required by law to call state agencies before you dig anywhere on your property.

Call 811 is the new national number for call-before-you-dig. It will put you in touch with your state's call-before-you dig agency.

http://www.call811.com/

Look here for state specific information:

http://www.call811.com/state-specific.aspx

If you dig and damage any utility lines without first calling and getting permission to dig, and having each utility come and mark on your property precisely where the buried utilities are located, YOU will be held legally liable for any damage you cause to the utility lines: sewer, water, telephone, cable TV, electric, etc... even if these lines are located within the bounds of your own private property.

You will be required to pay for any damaged utilities and will be additionally be fined.

In my state the fines start at $1500 per offense and quickly go up from there.

If it is a utility line then it is most likely required to be deeper than 18" through private property.
In fact, if this is a distribution line actually feeding 93 homes then it should NOT be running through the middle of private property.
If it is near the property line then it is most likely in a right-of-way that is not actually your property. Most roads are much wider than the actual pavement itself. They extend into the grass/property several feet.

Ali, can you give us some more detail that just "a cable running through my garden"?

I do not think this poster is from North America, and if so, all bets are off. Codes are not the same as US or Canada in other countries.