I had a VW Beetle many years ago, my first car, and it developed a corroded disc. The corrosion was caused by a faulty caliper, one pad was not being properly pushed on to the disc (fixed not floating calpier). This was because the car had been left standing for some time, a rust ring had formed between the piston and caliper. Due to the rust ring the pad/piston wasn't retracting properly causing the pad to wear away very quickly until it no longer was making contact with the disc. After the pad wore away was when the corrosion on the disc started to build up, i.e. it wasn't being scrubbed off by the friction every time I braked.

So I would expect if I was driving my car regularly and corrosion started to build up on the disc this would indicate the pad is not making contact with the disc, no friction scrubbing, and therefore it would more likely be a caliper fault and require the caliper, disc and pads to be replaced - typically as a pair across the axle to keep the braking effect balanced - as was required with my VW.

That's interesting, we use the car regularly, so long standing is not an issue, but as all discs are showing corrosion on the inner faces, maybe there is an issue with the callipers and the whole braking system

 

Good luck because I had a similar problem with my last Jaguar and they refused to budge.
I had warped disks causing steering wobble on braking. They refused to acknowledge disks should not warp and claimed it was wear an tear. They are notoriously reluctant to admit fault.

 

Just had Discovery rear brake pads and discs replaced on advise from LR garage after a service and it’s 2nd MOT. Told discs were pitted and showing corrosion. The car has done 35,000 miles and is a 2021 vehicle- We bought it from LR dealership at 2 yrs old (during Covid) where it was supposed to have had full checks etc. IT had its first MOT last year.
Had our geared Audi 15yrs and it’s still going strong with no issues on brakes and pads. Find auto driving a bit frustrating as brake used a lot where as on a geared car you can change up and down as speed control mechanism - maybe that’s why replacement seems frequent?
Interestingly - two other guys in the showroom were also having discs and brake pad work and one said his wife’s Discovhad also had to have discs replaced not long after he bought it.
Coincidence or issue? .

 

Plenty of other threads on these forums plus speaking from experience, highlighting that the discs are not fit for purpose under certain unknown circumstances. Cars a year old with 12k miles being presented back to dealerships with discs overly worn, corroded or warped. JLR’s response “does not affect performance and not covered by warranty as due to normal wear and tear”!
The dealerships are well trained now to not bother JLR on your behalf.
But also I now get my car MOT at Halfords as less chance they’ll make up advisories.