Hugh Townsend, of Exeter-based Townsend Chartered Surveyors, said many of the problems he had come across arose from annual short-term agreements like grazing licences that were due for renewal before the May 16 deadline for submitting SFP claims.
Often these were just casual agreements between neighbouring farmers, in some cases with no money even changing hands, Mr Townsend said.
This meant farmers were reluctant to take professional advice or draw up formal contacts.
But proper documentation would be needed by DEFRA to prove that whoever was claiming SFP on the land, the tenant or the landlord, was entitled to do so, he said.
This would be particularly important for landowners who wanted to safeguard entitlements by including the land on their own claim forms.
Some tenants were still not aware that they could claim all of the historic entitlements during the first year of the SFP without including all of their rented land on their claim form, he added.