The clip is a sort of almost one use. I am assuming you mean the sort of jubilee ring clip on the air pipe?
The way most people deal with it is they get the old one use (it can be reused but difficult) and measure its diameter...then go to halfords/supply place and buy a corect size jubilee ring and use that instead...makes for easier removal and refit at later dates. BMW also can sell the proper clip to you for a few pennies.
R