Rust front wheel arch

You should be able to have it repaired. It might be cheaper to replace it though.
Contact a specialist.

Repair would be futile....Once the old ferrous oxide has got that far, the ONLY way is to cut it away and weld in new pieces using new metal. I did this on my MGs. and a friends bay window. Once you have clean solid metal, you can then start to fabricate and weld(if making your own) or weld in new genuine replacements. RUST needs to be stopped and attempting any kind of quick fix will only let the rust spread.

yeah you could repair it but like MG said ,you ,if circumstances allow should remove and inspect/replace ,cheaper over the long term and if replaced remember to give it large on the rust prevention treatment afterwards