I'll grant you most people in the UK would say la bor uh tree and sek ruh tree (or sometimes sek uh tree) but I've never heard anyone here pronounce waistcoat as anything other than waist+coat - in fact I'm not even sure how else you could pronounce it!
Also: not everyone here pronounces their 't's. Londoners and most Southerners pronounce matter more like ma'uh.