The feed-in tariffs in the UK came into force in 2010 and serve the promotion of small plants producing electricity from renewable energy sources, as long as their power does not exceed 5 MW (Article 3 FTO 2010).

After completing the registration process, the current from the plant is fed into the grid and purchased by a licensed electricity supplier. The gas and electricity market regulator adjusts them annually. The feed has a term of 25 years. The Gas and Electricity Market Authority publishes the amount of compensation annually until 31st of March in an inflation-adjusted rate table (Art. 13 FTO).

Source: UK Department of Energy and Climate Change

In Great Britain there are often very short-term changes to the existing rates.
Please follow the link to the official regulations of the British Department of Energy & Climate Change.