UK or US, I have a hard time with getting a well-fitting waistcoat or jacket. Pretty much if it fits my chest, it won't fit anywhere else (waist or length). Of course, I'm in between standard sizes and don't need the extra allotment in the keg area. Even though I measure right around 39", a US 38" usually fits me (at least in the chest) because they're roomier.

So, for UK. I've ordered a waistcoat in a size that should have been marginally too small (a 38, but price was unbelievable), but it ended up swallowing me. Another waistcoat I ordered in 40 (as well as my two Argylls), and they all fit charmingly in the chest, if not elsewhere.

Compromise schmopromise. Custom is the way to go Then you know what you're getting.