The registry is to launch an information campaign this autumn to warn the two groups that they could face expensive legal fees if they fail to properly register their land.
While most urban land has been registered, a lot of land in rural areas of England and Wales remains unaccounted for. This is because the turnover of land ownership is much lower in these areas and the compulsory trigger points for registration - the sale or lease of a property, mortgaging or remortgaging - have not taken place, according to a spokeswoman.
PR activity will target mainly private landowners with more than 2,500 hectares and farmers with more than 50 hectares.
COI managed the three-way pitch that included Good Relations and Harrison Cowley.