As a Landlord you could be unintentionally letting out energy inefficient properties illegally

Energy performance certificates (EPCs) for houses in the UK are "incorrectly rated" in total by 15%, or 2.5 million, with hundreds of thousands of residences being "illegally rented" by landlords.

New research cautions that a "substantial proportion" of houses are below the legal criteria (Grade E) for rent since around half of EPCs are "extremely erroneous" that the buildings would need to be re-graded.

An EPC provides ratings to show a property's energy efficiency and environmental effect at the time of evaluation as well as what it may accomplish with suggested repair work.

More than 17 million EPCs have been registered so far; they are listed on the national register and are good for 10 years before needing to be renewed.

According to research by property technology provider Spec, landlords are renting out homes unlawfully since an estimated 35,000 E-rated homes, worth close to £8 billion, fall short of the requirements for the residential lettings market.
It was discovered that this was caused by EPC ratings that would probably be reduced if the floor space were precisely measured.

It demonstrates that one in four EPCs listed a property's size with an error more than 10% from the real measurement.
Floor space plays a significant role in the computation used by Domestic Energy Assessors (DEAs) to get an energy rating for a property.