Britain's security forces have been placed on high alert for a potential beheading attack by radical Islamists after a number of them were detected discussing a plot to target and kill British soldiers, police and members of the British intelligence community.

A deadly attack against a British soldier was feared on New Year's Eve when a jihadist Twitter account wrote: "Allahu akhbar! Islamic State [IS] has killed a British soldier in Britain in his own home." The claim was investigated by police and intelligence but was eventually ruled out.

A security source told The Times of London: "We thought, 'This is it, this is what we've been dreading.'"

The surveillance conducted by security services has unmasked private conversations between British jihadists and radical Islamists based in Syria about launching attacks on representatives of British authority, in similar fashion to the attack on Lee Rigby near a Woolwich barracks in 2013.

"It's a valid fear, probably the number one fear," one counterterrorism source told the newspaper.

"Our gun laws make it very hard for them to carry out the sort of attacks that happened in Paris. But we know from Woolwich that the stabbing or beheading attack is easy to do and hard to stop."

It has also been revealed that officers have been given the authority to advise soldiers against wearing any trace of military uniform outside of their barracks.

"It is down to local commanders and base commanders. A lot of the military don't want to be cowed into not wearing uniform because they see it as a sign of weakness," a Whitehall source told The Times of London.

The revelations come after reports that al-Qaeda's branch in Yemen has told its fighters that Britain is a higher priority than France, while armed police have increased their patrols around British Jewish targets following the attack on a kosher grocery in Paris.