Complex sentence: This left John Bedford Leno, his brother and a few others in the same cab, at the head of the procession, which was so vast that when the leading carriage reached Bond Street, the last had not yet left Holborn.
Split into simpler sentences: This left John Bedford Leno, his brother, and a few others in the same cab, at the head of the procession. It was so vast that when the leading carriage reached Bond Street, the last had not yet left Holborn.