Complex sentence: Pick wanted a new type of station for the Underground Group's Piccadilly line extensions and the designs he commissioned from Holden (1931--33) adapted the architectural styles they had seen on the tour and established a new standard for the Underground.
Split into simpler sentences: Pick wanted a new type of station for the Underground Group's Piccadilly line extensions. The designs he commissioned from Holden (1931--33) adapted the architectural styles they had seen on the tour and established a new standard for the Underground.