LONDON—Tech giant Google has spent $1 billion to buy a central London building where it is currently a tenant, showing its confidence in the future of the office as a place to work, the company said on Friday. Google, which employs 6,400 people in Britain, plans a multi-million pound refurbishment of its offices within the Central Saint Giles development it is buying, close to Covent Garden in central London. “We have been privileged to operate in the UK for nearly 20 years, and our purchase of the Central Saint Giles development reflects our continued commitment to the country’s growth and success,” said Ruth Porat, CFO of Google’s parent company Alphabet. Google said it would eventually have capacity for 10,000 workers at its UK sites, including one being developed in the nearby King’s Cross area of London. Google said last month that it was delaying its return-to-office plan globally amid growing …