Sorry, I couldn't find pricing data for that day. The closing price for Bitcoin (BTC) in terms of GBP on September 8, 2017 was 3,226.82. It was down 8.2% for the day.
DATE
OPEN
HIGH
LOW
CLOSE
September 08 2017
3,514.05
—
—
3,226.82
Daily pricing data for Bitcoin dates back to 7/13/2010, and may be incomplete.