In this image, David Niven wears a single-breasted Prince of Wales check suit with peak lapels - a look not uncommon during the middle decades of the last century. Nowadays we more commonly find peak lapels on double-breasted coats. Notch lapels (where the peaks of each lapel are roughly even in length) generally look more balanced on a single-breasted jacket.
However, the look is being revived. I saw several examples at the Savile Row London Collections: Men event at Lord's last year. In the lower image, taken at that event, the man in the right wears a grey single-breasted suit with peak lapels. Skilfully done, the look can work well - it certainly suited Mr Niven.
