Drain Pipes Crossing Farmland Agreement Example

[taffinnorfol]

Oh, the joys of higher water tables and old fashioned drainage systems!
We live in Norfolk and bought a house with an ancient cess pit for sewage! I won't bore you with the problems!!
We have just committed �10,000 for a sewage treatment system, which includes pipework across our, very obliging, neighbouring farmer's field, into a ditch (with the water authority licence, of course!).
We are now totally broke but the farmer has suggested that it would be in both our interests to have a legal crossing agreement in case damage accidentally occurs to the pipe! We're quite happy to take all responsibility as he has been kind enough to let us cross the field but we need to find a reasonable template / model / example agreement which we can both sign, have witnessed and then put with the Deeds.
Does anyone have any idea where I can get such a model agreement or, if not, some suggested wordings???
Many thanks!