BMW Rust/Corrosion Warranty

[bp1]

Took advantage of the good weather here(Glasgow) yesterday to wash/polish the car and found a bubbling on the drivers door. There is no damage to the paint surface I can see, but there it was, size of a 50p or so. Its a 2004 car, full bmw service history, whats the story with getting this sorted under warranty assuming there is one?

[bp1]

Thanks guys, I'll look in the log book and check and contact the local stealer.