No matter what title's used, UNDERWORLD INFORMERS or simply THE INFORMERS, it's right up front about those shady characters desperate enough to run to the law and name names...
Only here it's Scotland Yard's Nigel Patrick who takes foot after them... one snitch/snout in particular in a newly-slain informer's hard-working ex-con brother Colin Blakely, so intensely energetic he needed far more screen time...
But it's pretty boy criminal Derren Nesbitt on the freewheeling forefront, strutting his wealth as he and more cautious partner Frank Finlay hang in a crowded nightclub while their planned bank heist (after several previous knockoffs) occurs simultaneously elsewhere...
So Nigel Patrick's Chief Inspector John Edward Johnnoe... vulnerable to strict chief Harry Andrews since he cuts corners to begin with... dives into a dog-eat-dog plot saturated enough for three crime flicks while curbed by two dames that, like any Noir, has one naive the other wicked.
Unfortunately the gorgeous Katherine Woodville is benign and underused as the cop's wife, leaving the good stuff to bad girl/moll Margaret Whiting who, despite framing our hero, is equally sympathetic as a single mom mentally and physically abused by that rich pompous crime lord Nesbitt...
Who really has the most fun since, unlike everyone else... dizzy from all the complicated bedlam... he's grinning till the end, and with an unapologetic villainy that -- possibly inspired by the likes of Robinson and Cagney -- becomes downright infectious.