Buhari, who arrived the Nnamdi Azikiwe International Airport, Abuja at about 5:40am aboard British Airways, was received by party chieftains and supporters.
He told newsmen that he had taken some time off to rest after the campaign and was now back mentally fit to continue.
The APC flag bearer, dressed in black kaftan and black cap, spoke to journalists at the airport before he was driven into town in a motorcade.
Part of his engagement in the United Kingdom was the lecture he delivered on the "Prospects of Democratic Consolidation in Africa: Nigeria's Transition" at the Royal Institute of International Affairs (RIIA), Chatham House, London last week Thursday.
Buhari met with key stakeholders in British politics that included two former Britain's Prime Ministers Gordon Brown and Tony Blair, among other parliamentarians.
He also met with Nigerian professionals in Diaspora, youth and students organisations as well as granted interviews to some London-based media organisations.
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