Sure there's something perfectly obvious I've missed but ... why when I try to change dates on a reward booking am I being charged £25 change fee + £40 additional taxes, when exactly the same change would have cost me just the £25 change fee on Tuesday (damn my hesitation).

Have looked around at some other destinations I'd been considering and the taxes & charges charged are now significantly more than they were earlier this week (eg LHR-JFK is now over £500 - was around £470 on Tuesday). Can't be another YQ increase surely? Didn't we just have one?