Anti-terror gates which can stop a seven-tonne truck were deployed to protect the Queen for the first time as she attended a church service in Norfolk.
The portable barriers, made by a Belgian company, were erected on roads around Sandringham Church, where the 92-year-old monarch joined worshippers on Sunday.
The gates can be pulled into position in seconds if a suspicious vehicle fails to stop and heads towards Royal family members.
Pitagone, which makes the system, says it offers a 'unique and mobile solution against ramming attacks'.
It says it is quick to assemble without tools and 'stops the passage of vehicles even in a hostile situation'.
A Norfolk police spokesman said: 'We will always put practical and precautionary measures in place when policing events which attract significant numbers of people, such as the church services at Sandringham. We will not comment further on security matters concerning the Royal Family.'
More than 3,000 well-wishers packed into Sandringham Park, hoping for a glimpse of the Queen and members of her family at the Church of St Mary Magdalene.
The crowd is believed to be a record for a Sunday service. Well-wishers were searched before being allowed into the park.
The Queen arrived by limousine and the party attending the service included the Princess Royal and the Earl of Wessex. The Duke of Edinburgh was not present. Palace officials have quelled speculation about his health in recent days, insisting he is not unwell.
The 97-year-old Royal also missed the traditional Christmas day service.
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