The whole certified copy thing is a bit of a minefield, I've not truly figured it out. However, if you go to a notary public it will cost a small fortune; the last time I enquired, I was quoted: "85 pounds for the first document, and 35 for each subsequent", they also generally want to verify the authenticity of the original, not just certify the copy - it depends who you speak to, but I've found them a bit -erm- opinionated shall we say?
A solicitor can certify copies (usually at a price), as can the bank.. the minefield is figuring out what is sufficient certification for whom...
In your position, I'd pop into the bank at a quiet moment, see if they'll help, send the copy to the CAA, and hope they're happy enough with that..
What has everyone else done?