"I meant a 'folk style' "
Fine Andy - I accept that and have set out how I believe Ewan went about it - it's not by any means the only way but it seems to me a convincing use of the vernacular holds the key to an approach.
It's ironic that one of his finest songs is a mixture if a Sicilian tune, personal retrospection and Shakespearean references (chicks = Macbeth).
Forcing both the style and the language leads almost inevitably to pastiche - listening to how the subjects of your songs express themselves can help avoid this.
One of the distinguishing features of traditional song is that the people in them invariably have names and identities - quite often occupations.
Anonymity comes with your song taking on an identity of its own, as have a number of MacColl's; particularly among Travellers.
All the Traveller and West Clare songs we recorded were anonymous, even though most had been made within the lifetimes of the singers.
In the case of the Travellers, some of them were less than a decade old, yet the singers referred to them as "old songs" - a reference to type rather than age.
Anonymity isn't a defining feature - it's just commonplace to most folk songs.
Your aim should be to write a good song - I find the folk forms adaptable enough for that purpose, but they are bn no means the only ones.   
Many of MacColl's good songs didn't follow any identifiable style - he used jazz for his John Axon songs ans some of his 'Festival of Fools' (and one of his 'Singing the Fishing' compositions was based on Gilbert and Sullivan.
G'luck with your writing
Jim Carroll