This brass plaque was discovered during restoration of Eversholt Church in 1864. It is currently on display in the chancel. Click for a full resolution version.

I (EJW) hunted for similar images online and found this one, from the Norfolk Churches website run by Simon Nott: http://www.norfolkchurches.co.uk/blickling/images/dscf1349.jpg.
Thanks very much, Simon, for permission to reproduce. The picture below is copyright Simon Nott, please go to his site for reuse information.

That comes from this page , where it is labelled “Felthorpe Boys, 1454”. The Felthorpes were a Norfolk family. The engraving is remarkably similar. The pleats in the skirts, the folds in the arms, the hats, the collars, the shoes, the overlapping feet, the belts… I will try to find out more about that Norfolk picture.
I also looked at The Monumental Brasses Of England. Archive.org provides this picture of an individual in similar style:
The man has the same depiction of hair, collar, cuffs and feet, and similar pleats in his skirt. That picture is dated 1437, so the style definitely supports a date in the 1400s.
For photo information and image reuse, please see this page.