Dan Stevens at the 'Beauty and the Beast' London Premiere

Check out the button-one, single-breasted, peak-lapel, navy suit that Dan Stevens wore to the 'Beauty and the Beast' London Premiere.  I agree with Tom + Lorenzo that his look is bland, but it would be even more bland if the suit was a button-two.

New Anthony Sinclair Suit

In his latest post, Matt Spaiser of The Suits of James Bond showcases the button one suit he just had specially made from Mason & Sons, heir to the name of Anthony Sinclair, who was Sean Connery's tailor during his tenure as Bond. 

Gray Blazer

Front button style: button two

Button stance: classic (buttons at natural waist)

Jacket length: slightly short

Sleeve length: classic

Front darts: yes (slight waist suppression)
Color: medium gray

Lapel width: slightly wider than classic
Lapel edge: swelled
Lapel style: notch
Notch height: slightly high (but not high by today's standards)

Jetted or patch pockets: patch
Flapped or flapless: flapped
Flap height: classic

Cuff button style: button one

Vent style: single
Vent height: deep (11"; classic height is 8-10")

Shoulder: moderately padded and extended 

A Southern California chain that went out of business in 1991, so the blazer can't be any newer than that.

Age verdict: late-1960's (or very early 1970's), for 3 primary reasons:

1) the late 60's were a transitional period between the thin lapels of the early-mid-60's and the wide lapels of the 70's;
2) Deep vents started becoming popular in the late 60's;
3) Although the button one front reached its apex of popularity in the mid-60's, the button one cuff remained stylish for a couple years thereafter, even on button two and three fronts.