I would imagine CEDR or a court would take a fairly dim view of any company that made an offer then tried to lower it having never indicated there was some sort of time limit in place to accept - this isn't a quote or an insurance renewal where costs and/or risk might change. That smacks of the double glazing salesman who tries to pressurise you into signing because this is a one-day only deal, and whatever you might think of BA I'd seriously doubt it's sunk to the levels of someone desperate to close a deal to get their commission for the month.

Equally, I can't see any court increasing the amount awarded given the offer seems extremely generous in the first place, so I can very much see that any time or money spent taking this further would be wasted. I would, too, accept the offer and cut any perceived losses I might have.