There was lack of clarity over the reason for his detention at the airport.
According to one of the organisers of the function Ramdev is here to attend, he was questioned on books he was carrying which were in Hindi and Sanskrit. The officials detained Ramdev for over six hours before he was allowed to go.
However, a source said, Ramdev was questioned by customs officials as he came here on a visitor visa instead of a business visa.
Some media reports also said that Ramdev was questioned about certain medicines he was carrying with him.
Ramdev's spokesman S K Tejarawala described as "baseless" that he was questioned on carrying some medicines.
"It was not clear why the Yoga guru was detained for over six hours at Heathrow. He was not carrying anything with him except a small bag of personal effects. It is for the British authorities to explain why he was detained," Tejarawala said.
He said Ramdev has been cleared to go into the city.
Ramdev went to London to attend the function organised by the Patanjali Yogpeeth on the 120th anniversary of Swami Vivekananda in the next couple of days.