Air-con pipes on our cars are a bit hit and miss getting the correct pipe. There are a few different pipes available. If you contact MikeS through PM or if he sees this thread, he may be able to help you out as I'm sure he has a copy of EPC from Vauxhall and he'll be able to get the correct part number.
Which area is the pipe in? Is it the one that comes out of the bulkhead and then connects to another pipe at a valve joint and then wraps around the outside of the cam cover or is it one of the pipes lower down the front of the engine area?