there is no excuse for carrying around 1k worth of work on someones car without putting a 5 min phone call in to get the all clear. he could of had another garage lined up to perform the work, could be doing it himself, could have sourced aftermarket parts he wanted on.. there are loads of scenrios.
the rest of the thread just seems like confusion and a some excessive labour rates. the 'unauthorised' work is the problem for me.
But was it really unauthorized? Have we had 100% confirmation from OP that he was under no influence of knowing he was getting new discs?
nope, but the OP "The bill for this has come in at £1800! He said the brakes disks were also corroded and needed replacing but he went ahead and did this without telling me." seems pretty resounding evidence they didn't ask!!!