"We've been also negotiating with our friends and partners in the EU about Brexit and you know I'm still cautiously, cautiously optimistic," Johnson, with his hair ruffled, said in a film posted on Twitter.
He said "wonderful" climate change activists had been making a lot of noise with the "haunting, lilting melody of the saxophone wafting in over the Downing Street walls" as he exercised his dog late at night.
Johnson said the dog was in great shape.
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