Globaliser

I wonder whether trophy means that they tried to use the "hold the price" option.

A batch of fares expired last night and the replacement fares are indeed higher. Strange things can happen during the last few hours of a fare's validity, and (if this is what the OP was trying) I wonder whether that might have had something to do with it.

I can foresee a problem, though, in that the OP probably has no evidence that he was quoted any particular price yesterday or that there was an attempt to "hold the price".

[ETA:] I don't know what price the OP is seeing today, but I can easily get an N class fare in both directions at about £530. However, interestingly there are O and Q class fares filed which look like they ought to be valid for the random dates I've looked at in November, but I can't get either ba.com or ITA to price using them. If the OP could get the O class fare, there might be £60 off the price that I found, which could be a small consolation as it would be most of the way back to £434.

But in the OP's shoes, I'd have booked straight away (in the knowledge that the fare was about to expire last night) with the comfort of knowing I had 24 hours to change my mind and get a full refund.