It is a legal requirement that every property marketed to let have an EPC - an Energy Performance Certificate. It is important to note that it is the marketing and not the letting of the property that is the key point which invokes the legislation.
The theory (and to us it is very much a theory) behind this is that any applicant who wished to see some properties may ask to see the certificate in order to make their choice of rental property. The likelihood of this scenario aside, there is a fine of £200 and you will still have to get a certificate anyway after paying this.
We have seen a petition circulating, originating from an EPC company which asks that the EPC rating become compulsory in all marketing materials (for example portals such as Findaproperty) and we have heard rumours that this is being considered by government. If this is the case then it will become much more difficult to avoid.
In truth at around £70 and lasting for ten years it is not exactly a major expenditure and the ideals behind it at least are noble, being to focus everyone on the environmental cost of the way we live and to encourage conservation. For this alone it is probably with the cost and hassle, nevermind it being ones legal duty as a landlord or agent.