Dozens of protesters, comprising both Malaysians and foreigners, gathered outside Mansion House at London an hour before Najib's arrivalfor a meeting with the London business community.
Yellow posters and banners, condemning the clampdown on Bersih 2.0 were unfurled, urging the Malaysian government to release six Parti Sosialis (PSM) activists dubbed "EO6" being held under the Emergency Ordinance which allows indefinite detention without trial.
According to theSarawak Reportportal, Najib in a big convoy gave a cheery wave as soon as he spotted the crowd.
It said the protest went off peacefully with the policing minimal and friendly.
According to a protester, PKR youth leader Ginie Lim the police deployed a truck to block the protesters from the view of the delegates attending the meeting.
Yellow begins to reign supreme
There was another peaceful protest at Downing Street, London, where the official residence of UK Prime Minister is located. Najib was there to meet his UK counterpart, David Cameron.
Both leaders signed a memorandum of understanding on enhancing strategic cooperation to combat trans-boundary crime and international terrorism.
Protesters in yellow clothes put up posters, in matching colour, that read "Shame on you, Malaysia PM, clean and fair election and free our leaders now".
Another protest will be called at the Inter Continental today in UK time 7pm where Najib is expected to attend a function.
Before the meeting with Cameron, both Najib and his wife, Rosmah Mansor, had an audience with Queen Elizabeth II yesterday in Buckingham Palace, who coincidently wore a bright yellow dress.