Last year I took part in a debate on ­sustainable, or ‘green’ leases, at one of the events organised at the Law Society by Pamela Castle OBE, chair of the National Centre for Biorenewable Energy, Fuels and Materials. It brought together scientists, lawyers and policy makers in public debate. Also on the panel were Jon Lovell, head of sustainability at Drivers Jonas Deloitte and Andrew Stunell MP, parliamentary under secretary of state at the Department for Communities and Local Government.

We engaged in a lively debate on the processes by which we might transform the existing built environment into one which is more sustainable.

From the legal point of view, the problem could be described as follows. In spite of significant reductions in the carbon footprint of new buildings, the vast majority of commercial premises were built before concerns about ­climate change and other environmental pressures began - via building ­regulations - to drive innovation towards green buildings. Of this ­existing stock, much of it is leasehold so that, in considering its upgrade or adaption to reduce environmental impact, ­significant problems arise in terms of how the burden of this might be ­allocated between landlord and tenant.

In fact, worse than that, survey work by my colleagues at the Welsh School of Architecture has shown that these responsibilities need to be shared by a large number of parties in multi-­tenanted buildings. Yet, even if little can be done about design and ­construction of existing buildings, good practice during occupancy can achieve a great deal. This is a commercially important issue now that commercial buildings are rated both by energy performance certificates introduced under the Energy Performance of Buildings Directive (2002/91/EC) and wider environmental impacts through the Building Research Establishment’s BREEAM ­standards. Property investors may take these performance levels into account and ­companies may want to be seen to be occupying commercial premises with good green ­credentials.

As with many issues on the ­sustainability agenda, there are gains for all parties in co-operation. For the landlord, a tenant known - through its annual reports - to be committed to strong environmental performance is likely to engage in best operational practice in its occupation of the building. At the same time a tenant may be attracted by a commitment on the part of a landlord to the efficient ­delivery of services and facilities. In this context, and given the multi-­occupancy problem referred to above, commercial leases may have a crucial role to play in delivering mutual ­benefit.

However, moving to a lease with a dark green hue may prove too great a step and there may be interim stages; gentler forms of agreement that one might consider. These softer ­agreements may prove helpful, also, where the parties are locked into long leases. A start might be an ­environmental management plan, because changes in the management of a building may be the key to improving the environmental, ­economic and social sustainability of the building. Such an agreement is, admittedly, easier in single-­tenanted buildings, but actually the benign ­influence of the behaviour of one ­tenant upon another may make good ­management practice even more ­crucial in multi-let ­buildings.

In this context, the Better Buildings Partnership (BBP) has been promoting Green Building Management Groups - designed to bring the owner, occupiers and building management representatives together to take control of the resource use in their building. The idea behind such groups is to create a forum to oversee the environmental performance of the building and to work towards the better and more efficient operation of the building. The presence of the group not only offers the landlord a chance to demonstrate current operational performance of the building, backed by data, but ­tenants can review their relative ­success in managing their occupation, hopefully resulting in a lower ­environmental footprint.

This activity can lead to or be ­supported by a memorandum of understanding (MoU), signed by group members, under which the operational management of the building is agreed with a view to improving its environmental performance. Since such a memorandum will not be considered legally binding, it offers the type of flexibility which may be difficult to achieve under a lease. It does represent a written commitment to pursue environmental improvement, however, and it is much more easily adapted to drive forward the targets than the provisions of a lease. BBP provides a template for a memorandum of understanding to promote agreement between owners and occupiers, and it covers a wide range of services (including water and waste ­management) and parties (such as contractors or suppliers).

These softer forms of agreement are seen as easier to achieve than green leases, though they may be a step on the way there. A green lease will take the form of a standard ­commercial lease but with added ­provisions aimed specifically at the management and improvement of the environmental aspects of a building. As with leases more generally, it will place obligations on both owner and occupier, and these will set out in some detail the shared environmental requirements of the parties to the leases for a ­building.

The ideal is that by starting with the same green heads of agreement in lease negotiations, the tenants ­occupying a multi-let building will face broadly equal obligations to meet ­environmental standards, while this endeavour is supported by the ­landlord through the provision of ­efficient services and the regular flow of information on the building’s ­performance. A lease could exhibit many shades of green in terms of the nature of the obligations and the ­consequences of breach though, again, model form green lease clauses from BBP provide a good starting point.

The debate on sustainable buildings demonstrated the pressures, both legal and financial, to improve the ­environmental and energy performance of commercial sector buildings. Landlords and tenants can work together to benefit from the enhanced performance of commercial buildings, and property lawyers can utilise a range of soft and hard law ­instruments to facilitate this.

Professor Robert Lee is co-director of the ESRC Centre for Business Relationships, Accountability, Sustainability and Society (BRASS) at Cardiff University; and a director of the Environmental Regulation and Information Centre. Get details of forthcoming Castle debates.