The Green Deal is a government initiative designed to reduce carbon emissions and save energy. The start date was 28th January this year. The idea is that, if residential properties can be more energy efficient then energy demands will be reduced.
The Green Deal allows property owners to pay for the energy improvement measures they make with no up-front payment. The householder will then repay the cost over many years, through an adjustment to their electricity meter but will have the benefit of the savings made due to their reduced energy requirements.
The following link will take you to the relevant page on the government website.
However, we can see potential issues where a property subject to the Green Deal changes hands. The buyer will have made an appropriate offer taking into account the works that have already been carried out and will be understandably reluctant to pay off the remaining cost. He/she may then seek a reduction to the price or require the seller to pay off the balance at completion.