Cusco:
A lot depends on the following:
1. If it will bisect a nice efficient field for him and mess up his crop sprayer efficiency.
2. If he likes you!!
3. His (if any) concerns about his neighbours and any noise.
4. Whether it will affect his enjoyment of his land and his liability risks.
Piper is correct that he would lose his £80 per acre subsidy, and the £100-£150 per acre farming margin. So, let's say he loses up to £250 per acre in income, that's £1,500 of lost income on 6 acres. He would want some hassle factor payment too, so you'd be looking at at least £2,000 per annum I reckon.
He will have good productive land in East Anglia, so it's not the best place to be trying to persuade a farmer not to plant it!! If he was on cr@p land in Gloucestershire or Wales, he'd probably snap your hand off at £1500!!!