Metropolitan police have installed towering yellow bollards near Buckingham Palace in the aftermath of the Westminster terror attack.
The bright arches, as well as steel barriers on the Mall, appeared overnight on the paved area linking Green Park and Constitution Hill just a few hundred metres from the royal mansion.
A Buckingham Palace spokesman refused to comment but Scotland Yard says the barriers have not been installed because of any intelligence.
"There is no intelligence to suggest a threat to these spots," said a Met Police spokesman.
"It's security measures put in place but not in response to any threat. Buckingham Palace is obviously a high profile area that is going to benefit from them."
It follows two seven-tonne armoured Jankel police vans - dubbed the "Guardians" by officers - being stationed around Parliament Square.
The vans can withstand rounds from AK47s, grenades and IEDs.
Adrian Ajao, who also went by alias Khalid Masood, killed four people, which included stabbing to death 48-year-old Pc Keith Palmer, on Westminster Bridge and outside Westminster Palace on Wednesday.
A former close friend has told how the 52-year-old father-of-three had long harboured a "blood lust" and sought professional help over his urges to kill.
MPs warned last month that there was a Parliament weak spot putting officers at risk.