By Nicholas Earl Blackstone will build its new European headquarters in London at its Mayfair base, in a fresh post-Brexit boost for the for the capital. The world’s largest alternative asset manager will occupy the redeveloped Lansdowne House – which will be refurbished into 226,000 square foot, ten-floor building on Berkeley Square. The decision to fully lease one of London’s premier office buildings reflects it commitment to further growth in the region. It also highlights the company’s rapid growth rate, as its London headcount has doubled over the past three years, now standing at more th…