I know its something they can suffer from but can anyone tell me how common it is within the breed
Archer

Have known a fair few Archer.  Its more common in those with a poor turn of stifle, than those with good ones. 
Dawn.

There is a hereditary link in Cruciate problems. The ligaments should be flat so strain is taken evenly by both. Sometimes the joint is sloping which puts all the load on one end of one ligament which, with a small twist of the dog can be overloaded and tear.

I think most Cruciate problems are from "natural causes" but if a pattern starts to emerge in certain lines then the hereditary side should be looked into.

Regards, John