A quick question about British economy

I've been through a book by Russian economist Lomakin. The book covers the economic aspects of the development of the UK in 21 century. It was published 5 years ago.

As proof I attach a page with highlighted sentence that stirred my interest. Since the book is in Russian, and I doubt there are many Russian speakers around here, I translate what it says. Basically,  it says that British companies have a higher stake in international division of labor than any other country. The sales revenues of oversea companies amount to 50% of British GDP, compared with only 30% for the US.  Now I wonder what exactly this means. Does this mean that foreign branches of British companies provide up to 50% of British GDP from their assets abroad, or perhaps foreign companies with branches in the UK contribute to British GDP up to 50% in revenues generated through sales in the UK, or both?

Thanks.  

Foreign owned businesses like Nissan, Toyota, Honda, Vauxhall, and now Rolls Royce Car manufactures that pay UK corporation tax, pay UK income tax, pay UK VAT, pay wages to UK workers, pay employers’ National Insurance contribution, pay workers National Insurance, pay UK business rates, and generate economic activity in the UK.