Spokesperson Garba Shehu says Buhari isn't in London to consult his doctors.
The 75-year-old Nigeria president has been tending to an undisclosed ailment since he assumed the reins in 2015.
In 2017, Buhari spent more than 100 days in London on a medical vacation.
Before his 2017 London trip, Buhari visited the UK on February 5, 2016 and June 6, 2016, for medical reasons.
Soon after declaring for a second term in office on April 9, 2018, Buhari left Nigeria again for London; this time for a series of meetings a week before the Commonwealth Heads of Government Meeting (CHOGM).
There are speculations in certain quarters that Buhari’s latest trip to London has everything to do with keeping a date with his doctors; even though the presidency sent out an itinerary as soon as it was formally disclosed Buhari will be travelling.
But Shehu told the BBC that those rumours are wide of the mark.
“President Buhari is in excellent health. In fact, I would say the president is a lot healthier today than he was when he took office”, Shehu said.
A couple of seconds later, he was repeating his lines for emphasis. “The president’s health is excellent. I am saying that it is excellent. He looks much healthier now than when he came into office”.
When the BBC asked Shehu why Buhari had to fly to London a week ahead of the CHOGM, the president’s spokesperson said: “There is a schedule that has been plotted out. And come to think of it, the relationship between Nigeria and the United Kingdom is intense; it is wide.
“And so the president has chosen this time to engage not only with the British government but a lot of common interests that bind United Kingdom and Nigeria”.
Buhari is expected back in Nigeria when the CHOGM ends on April 20, 2018.