Why Warhol?: Trader who ploughed millions into art collection

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Media captionPrivate Warhol collection of portraits goes on display

One of the most important private collections of the works of Andy Warhol is going on display at the Ashmolean Museum in Oxford.

A large part of the collection consists of portraits by the celebrated American artist.

I meet the man who owns all 140 works in the collection - Andy Hall, a commodities trader whose private art collection exceeds 5,000 pieces.