LONDON, Oct 15 (Reuters) - Britain's National Grid said electricity supply margins were likely to be tight in the country over the next few days but said it would have adequate supply.

National Grid is responsible for ensuring supply and demand are balanced in Britain's energy systems.

"Unusually low wind output coinciding with a number of generator outages means the cushion of spare capacity we operate the system with has been reduced," National Grid Electricity System Operator (ESO) said on Twitter.

The grid has a number of tools to help balance supply and demand and paid power producers such as nuclear generator EDF to reduce output over the summer when demand was weak.

"Margins are adequate for (Thursday) and we're monitoring how the situation develops," National Grid ESO said.

Gas power plants were supplying around 55% of the country's electricity on Thursday morning, with nuclear at 16% and wind at 15%, National Grid data showed.

National Grid ESO did not immediately respond for comment on Thursday morning.

(Reporting by Susanna Twidale; Editing by Edmund Blair)