Bar Width

Maybe a silly question but what is the max recommended bar width on a carbon fork/carbon steerer. Currently my bars are 800mm and need to be cut. I like a wide bar but the LBS said they may damage the steerer as at present there is quite a lot leverage and the fork slightly flexes side to side. I know they are cut down for comfort to fit the rider but I am quite tall and like a wide bar. I am a bit worried as the forks cost quite a bit. Any info?

Probably best asking the manufacturer of said forks, but 800mm bars aren't uncommon on alloy MTB steerer tubes; carbon is going to be just as strong if the stem is clamped correctly and you're not running a silly amount of spacers on it.
Also once you're riding that flex moves the bike, so it's not static flex. Is this a fixed gear you're doing tricks and stuff on? I'd be hesitant of that on a carbon steerer, more than wide bars on a carbon steerer being ridden normally.

Thanks for the info. It is a fixed gear bike but just for general riding. I will be getting the forks cut as they are just to wide. Also they look a bit silly too. I have just got to work out the right size to have them cut.

Ignore them, have whatever width you're comfortable with

As @PhilDAS says run them however you like them. Just pop on some bar tap and bar ends and go for a ride or six, your hands will end up where they end up. I had 820mm bars on my langster for quite a while (alloy steerer though) I didn’t do a die.

Does this bike get ridden in traffic?