Can I cut back a Precast Flue (ed. ? Or fireplace?)

[wiltslw]

Hi ...I'm new to the forum and wanted to ask if anyone had ever trimmed back precast flue starter blocks so they are flush with the wall? I had a builder round who said it would be too dusty and difficult to cut and i would be better off removing them. This would mean a lintel is required whereas trimming wouldnt...i assume. Has anyone got any opinions? Much appreciated.

 

[lostinthelight]

Whats your plan ?

 

[wiltslw]

Ideally to cut them back and block in the hole, leaving a vent at the bottom, and hang an electric fire along the wall.