How can we block off an unused external boiler flue?

[ACrawc]

We had a boiler in an old shed adjacent to the house.
The flue is encased in a brick chimney stack that runs up the outside of the house.
Some years ago, the boiler was moved inside, but the old flue remains. It looks like a chimney but is open at the bottom and unsightly. I am not sure whether it is lined with asbestos. Either way, can it simply be blocked in or bricked over at the bottom to make it look better?

 

[firemant]

Brick it in but fit a small air vent to help prevent condensation. The condense can eventually cause staining.

 

[WC1]

The soot left in the chimney tends to absorb water, as above make sure it's well ventilated.

 

[Knappers]

With a classic chimney youd cap the top with a slab and a gap for ventilation and brick up the bottom with a small vent to avoid damp issues (as above)