I've a job on a house where the brickwork is dropping above an aluminium
door (with a window at each side) in a cavity wall. I assume there is a
concrete lintel inside, but the door, which seems to have replaced a
similar timber version on the outer skin, has no lintel above, just a
plastic cover-strip glued on!! The opening is nine bricks long. The
three courses above the door are coming down, above is currently OK by
the look.

What sort of lintel can I put in to keep the bricks in place? There's
no great load, and I don't want the lintel to be externally visible.
A piece of galvanised angle-iron would do, but is there a "proper"
lintel available for this I'm going to knock out three or four
courses above the doorway, using a strongboy or just an acro to hold
up the courses above, put in the lintel, and brick up.

Any ideas?

J.