• duration: how long is the overage agreement to last for?
• planning application: insist on specifying the extent of the involvement of each party in the planning application; should there be specific time limits (or an obligation to use best endeavours); should there be provisions for progress reports and copy documents; consider an obligation to maximise the value of the land (and to apply for the most valuable permission); and should there be an obligation to appeal (perhaps subject to the view of counsel on merits)?
• planning permission: this may well be defined as a trigger event. But, are you referring to outline or detailed permission? What about onerous conditions, and what if the permission is obtained by a third party (not the contracting parties)?
• trigger events: apart from planning, what other events might trigger payment? For instance, this might be on disposal (in which case define precisely what that means – and assure there are provisions for any sale to be arms length, and not a collusive sale);
• the overage amount: it may be a fixed sum (should it be index-linked?), or perhaps a share of profits (consider an obligation to keep accounts, and consider what happens if there will be more than single payment). If there are references to ‘market value’ then consider provisions dealing with special purchasers (eg collusion), vacant possession, encumbrances, costs of complying with planning obligations, and whether there should be disregard in respect of other rights or land held that affect the planning position;
• less favourable development: should there be a clause to deal with the situation when there are unexpected problems (eg changes in legislation), with a reduced overage payment in those situations?

This is merely a taster of the problems that can arise. There are other issues to be considered such as interest for late payment, drafting of positive covenants (eg gifts, deaths, leases and charges to be dealt with), and what restrictions should be on the title; what releases should be given, and should the unpaid vendor’s lien be excluded?).

As we have said before, overage is a complex topic and is not for the inexperienced. If in doubt, take specialist advice.