Urchaidh said:

in general I don't think you
need any more 'bricking up' than simply reinstating the surrounding
brickwork. If the top of the beam would just be sitting free then I'd
suggest two resin anchors (or rawlbolts, but I'm a convert to resin
anchors) into the padstone.

The beam is to be installed perpendicular to the walls at each end and
supported on the "inner leaf". This is to allow removal of a single block
wall (which spans the width of the room) used to support ceiling joist
joints.
As this forms remodelling of an existing extension, this means that one end
sits on the original house outside brick wall and the other on the internal
extension block wall.

By bricking up, I meant reinstating the brick/block work around the beam
end, particularly to give restraint to the top flange of the beam. This
would I expect make the use of resin anchors or other fixings unnecessary.

What measures did you take for fire protection?
Is there some paint that can be applied?

Phil