Campy centaur FD work with double or triple?
 

I am looking at buying a set of derailleurs but the front one came on a bike with a triple chainring. Would this work with a double or should I look elsewhere?

A triple FD is not ideal, but it would work. A triple cage mounts a little higher and it may require one more click to to shift between the chainrings, due to the wider cage. FDs are relatively cheap, so I'd look for a double model. Campy double FDs have all been compact and standard crank compatible since 2008.

As DaveSSS says you'll get marginally better performance with an FD made for doubles, but it won't be a world of difference. After all the two larger chainring sizes on most triple setups are the same as they would be with doubles, so the FD's are designed around that.

I suggest that since you already have it (it's free so to speak) you should mount it and see if you're happy with it's performance. If so, used the money you've saved to buy yourself a few beers. Worst case is you'll decide to buy the double after all and will have wasted a bit of time, and of course, no beer.