i would like to hang a heavy metal gate straight into the brickwork of my house 30kg?

you have a basic problem -- brick [and all other masonry products, including mortar] is strong under pressure [pushing together] but weak under tension [pulling apart]. The weight of the gate will inherently try to pull the upper attachment out of the brick and pull the brick out of the wall.

the best way to get around this is to install a long mild steel bracket flush up against the brick wall so that it rests on the foundation or ground. A small 'shoe' on its bottom end may be desirable. The gate would then hang from the bracket. [Local machine shop can fabricate the bracket for you.]

this will transfer much of the dead weight of the gate to the ground or foundation as a pressure force and thus reduce the pulling out of the wall tension force the gate applies to the brick.

Overachievers could fabricate a flat bottomed "U" shape frame for the gate so that the entire weight rests on the ground and the welded steel of the frame corner carries the pulling out of the wall tension load instead of the brick. Then the brick wall is used only to retain the frame in its correct location.

[One assumes there is or will be a post or something on the side away from the house. The gate could also be hung from this post instead of the brick of the house.]

You might consider drilling all the way to the house framing and use lag bolts to attach the hangers to the house framing.

Bricks and gates don't mix. The opening and closing of gate will eventfully have the brick come loose from the mortar. Any chance of putting in a metal pipe or wood post next to house to mount gate on?

Brick you say? You can secure it directly to the house, I have seen it many times. I personally would not though, not for something with constant moving and such. I would secure a brace to the brick and then secure the gate to that.