Utilize the input text as a context reference, choose the right relationship between Vodafone and London from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

The London firm advised last week that " m ore of our European businesses are returning to growth ," and a 1.5% decline in organic service revenues during April-June indicates the vast strides made over the past year -- Vodafone saw European revenues droop 4.7% during the 12 months to March.

Answer: headquarters_location