XAUGBP is the price of one troy ounce of gold in pounds sterling, derived from XAUUSD divided by GBPUSD. It is the correct performance measure for a UK trader with a sterling account.
The sterling leg tracks Bank of England policy, UK CPI and wage data, gilt yields and UK fiscal news. A weaker pound lifts XAUGBP mechanically, which is why gold often records highs in sterling before it does in dollars.
London is the home of the physical gold market and the LBMA benchmark auctions fall inside the London session. The best windows are the London open (07:00 to 09:00 UTC) and the London to New York overlap (13:00 to 17:00 UTC), though spreads are materially wider than XAUUSD.