Defence Secretary Philip Hammond was challenged in the Commons to explain the UK's plans to monitor its coast from outside threats aside from "relying on Twitter" for intelligence.

Mr Hammond told MPs the UK had not been surprised by Russian vessels passing off the Scottish coast, adding they had declared their deployment on social media sites.

HMS Defender was ordered to sail from Portsmouth to waters north of Scotland to escort a Russian warship, Admiral Kuznetsov, and the rest of a task group, the Commons heard.

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Mr Hammond claimed it was "entirely false" to suggest the UK had been caught unawares by the Russians or there was a stand-off when the vessels passed through the UK's area of interest between December 28, 2013, and January 10.

Conservative MP Sir Gerald Howarth joked he was "immensely grateful" for the role played by social media in providing intelligence to the UK, as he pressed for a replacement to the Nimrod aircraft.

Shadow defence minister Kevan Jones also asked Mr Hammond how the UK would plug the gap in maritime surveillance "apart from relying on Twitter".

Mr Hammond insisted the issue would be examined in a 2015 defence review and drones could be one option.

In answer to Sir Gerald's point during defence questions about the Nimrod replacement, Mr Hammond told the Commons: "I wouldn't disagree with your assertion that we need to look at how we provide maritime surveillance cover and that will be part of the 2015 strategic defence and security review."