I use my Avios miles to upgrade from PE to club when available and have noticed a very large increase in taxes.
Today I checked this online before upgrading LHR to BKK. The cost should be £41.30. I cannot upgrade on line as it is a multicity booking. Did the upgrade over the phone and was quoted £82 as the difference in taxes. I queried and the agent said she would check with the fares department. It appears ther is an error in the system that charges additional taxes for BOTH ways even when you upgrade only ONE way.

I wonder how much extra money I have paid over the last few years for this error in the system?