I have had 200% boni from
32Red in the past, but they are pretty rare. The Club Rouge birthday bonus is now 200% (£250 for £500 bonus), when it used to be 100% (£500 for £500). It's also the norm for 32Red to "eat" their own mistakes, yet they are apparently willing to burn a reputation built up for over a decade over a mere £25K.
The emails shown by the OP do seem to back up the claim that there isn't really any more to this than some CS rep cocking up in crediting a 200% bonus instead of a 100%. We know from experience that when a CS rep gets it wrong, and is challenged by a player, they can often defend their wrong decision by saying things like (I work here, I know my job, what you got is correct, etc)
However, 32Red have already been changing focus away from players and towards the profit motive. They have stopped weekend payments in the face of discontent amongst players, and used a BS reason for doing so. They then removed "auto flush" from their system so they don't even have next day payment by default any longer, players now have to email CS to get their withdrawal "flushed".
There is a down side to jumping straight to court action though. The case for the OP would be stronger if they had pursued all possible avenues between an internal complaint and court action. At the minimum, a complaint through eCogra and/or a PAB here should be tried first, with action being taken in the courts only if a mutual settlement could not be agreed. The OP has already made his initial offer, in that he will allow the incorrectly credited £1000 to be deducted from the value of the claim.
With the new UK regulations imminent, this could be an interesting case if it is judged by a UK body, such as the court or the UKGC (assuming 32Red now has it's continuation licence, and the process of issuing the formal licence is under way).
The bolded term also works in the player's favour, as if the casino can indeed change the terms "at any time", it could be interpreted to mean that they changed the big bankroll bonus to 200% "at any time", and so far from being a mistake, being given 200% was consistent with this term.
Lastly, if such amounts are "never given", how come front line CS didn't find themselves locked out from doing this at their console. There are many instances of players contacting CS, who agree that the player is in the right, but that the player will have to wait till "office hours" because the agent doesn't have the required permissions to apply the agreed resolution at their console.
I would also expect the CS supervisor to get a right bollocking for making the initial mistake that created this mess in the first place. It would have been better to have paid up, and then dealt with the CS department internally. There would have been every chance of winning the money back off the OP given that choices have been squeezed by the new UK rules, and it would have made for some good PR from the story that a UK player had to move to 32Red from a casino that shoved them out the door because of the UK changes, and the first experience was being treated like a king, and then winning £25K and getting paid within a couple of days.