Would this be resolved by using the rigid style insulated flue. Costs an
arm and a leg but must be cheaper than bricking back up through the
loft?

Two downsides I can see, would look odd on a Victorian house, and
would require some rather good lead flashing to make a good seal
around a non-standard roof penetration (i.e. you can't use a standard
lead slate, nor can you cut and tuck lead sheeting into the
brickwork).

OTOH it must be done routinely where these pass through roofs (rather
than through walls) where there is no chimney to use at all. I haven't
seen the detail of how that is usually done though.

For that matter, if the stack has been taken below slate/tile level -
it will still require someone with the art of leadwork to make good
around a brick chimney.