The Ministry of Defence is to recruit a new force of "cyber reservists" to bolster Britain's online defences amid warnings of the dangers of an attack which could cripple the computer systems controlling vital national infrastructure.

The first annual update of the Government's cyber security strategy disclosed that all three services were now bringing in additional experts to support their work protecting against the growing threat of cyber attack.

Details of the new cyber reserve force will be announced by ministers next year.

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The MoD has already established a military Joint Cyber Unit based at GCHQ – the secret electronic communications spy agency – in Cheltenham.

The strategy document said it was now developing "new tactics, techniques and plans to deliver military capabilities to confront high-end threat".

Publishing the document, Cabinet Office Minister Francis Maude said: "There exist real and growing threats to our interests in cyberspace."

The move comes as officials disclosed that "hostile foreign states and others" had carried out "mapping" of the systems controlling UK critical national infrastructure – such as power and water supplies.

The officials would not name the countries involved although reports in the US have said Russia and China have carried out similar "reconnaissance" exercises there.