Contestability refers to the fact that you can choose your electricity and gas suppliers. Although this may sound good, in the short term it is causing big price rises (of the order of 30% or more). The reason for this is that the electricity generators can charge massive prices when we have a peak demand (ie on a hot afternoon). Organisations that use a lot of their energy for air conditioning (like hotels and offices) are being hit particularly hard. This needs to be taken into account when planning any major air conditioning changes. It also means it may be desirable to have an air conditioning engineer involved when you negotiate with the suppliers.