The Department of Energy and Climate Change collects numerical information relating to gas and electricity security of supply. The data are available on an annual basis in DUKES (Digest of UK energy statistics). Quarterly and monthly data are also available at the following websites (where the corresponding tables in DUKES can also be found).
http://www.decc.gov.uk/en/content/cms/statistics/source/electricity/electricity.aspx
http://www.decc.gov.uk/en/content/cms/statistics/source/gas/gas.aspx
The key tables in DUKES are as follows:
Gas
UK gas production and imports: Table 4.3
Origin of imports: Table 4.5
Capacity of gas storage sites: Table 4.4
Gas consumption in the UK: Table 4.2
Electricity
Fuel mix used in electricity generation: Table 5.6
Plant capacity: Table 5.7
Plant load factors and maximum demand: Table 5.10
Electricity consumption in the UK: Table 5.2
The Department also releases information relating to energy consumption by sector and end use; these data are available from the Energy Consumption in the UK section of the Departments website at:
http://www.decc.gov.uk/en/content/cms/statistics/publications/ecuk/ecuk.aspx
In addition, the Department receives information from National Grid on electricity generation and network capacity and on gas flows and capacities which are referred to in Energy Markets Outlook.