Charges seem to vary from hour to hour.
I recently checked fares and charges for a BA LHR to Barcelona return flight at 1900 checked a few other fares but did not make the booking. I returned to the task at 2200 and booked the BA flights but amazingly the charges had increased by just over £11 for two pax.
I rang up the next day and was told that " the fuel surcharge can vary from hour to hour". Is this true.....sounds a bit far fetched to me!!!!!