Gotta be honest, I don't know what Cedric' dialect or accent would sound like. Cedric is an old English name, so would a sharp English accent be in order?
Depends what you mean by 'old English' - Cedric actually being invented by Sir Walter Scott for a character in his novel 'Ivanhoe', though based on the possibly Brythonic name
Cerdic - meaning, in short, that he'd probably sound quite Germanic, as that is what Old English is. If on the other hand you mean 'sharp English' as in upper class/RP English, then he'd sound more like a 1950's newsreader or the Queen.
To be honest, given the time period setting of this RP (roughly 1200s to 1400s), he'd pobably be speaking like Geoffrey Chaucer; here's a little example of his work from his famous
Canterbury Tales...
"Whan that Aprill with his shoures soote
The droghte of March hath perced to the roote,
And bathed every veyne in swich licour
Of which vertu engendred is the flour;
Whan Zephirus eek with his sweete breeth
Inspired hath in every holt and heeth
The tendre croppes, and the yonge sonne
Hath in the Ram his halve cours yronne,
And smale fowles maken melodye,
That slepen al the nyght with open ye
(So priketh hem nature in hir corages),
Thanne longen folk to goon on pilgrimages."
- (General Prologue, 1–12)
To summarise, I wouldn't give too much of a worry and, unless you're very much wanting to be 'time accurate', I'd just stick to modern English. Being as you say a 'common peasant' though, it is probable that he'd be using simple words, being unable to read or write, and have difficulty understanding people using flowery language.
Dialect wise, well, you'd need a distinct area of Britain to find that out - contrary to popular belief, there is no 'British/English accent'.
Hope this helps, if you've got any questions then feel free to ask.
