The only additional useful thing I can think to add to JtH's good advice is to copy and paste the wording of the relevant s215 - so at least you know what you are up against. This is it:
s215 : Power to require proper maintenance of land
(1)If it appears to the local planning authority that the amenity of a part of their area, or of an adjoining area, is adversely affected by the condition of land in their area, they may serve on the owner and occupier of the land a notice under this section.
(2)The notice shall require such steps for remedying the condition of the land as may be specified in the notice to be taken within such period as may be so specified.
(3)Subject to the following provisions of this Chapter, the notice shall take effect at the end of such period as may be specified in the notice.
(4)That period shall not be less than 28 days after the service of the notice.
What's probably more important to you is what the penalties are for non-compliance. This is covered in s216 (unsurprisingly). I won't copy and paste it as it is rather long, but you can view it here:
http://www.legislatio...8/section/216/enacted
The level 3 penalty that it refers to is currently a maximum of £1000, as far as I can work out.