How to cut this waste pipe?

Hi,
I am in the process of removing a sink (see pics below).

I am going to temporarily cut the hot and cold pipe, and cap them, and then later raise the floorboards and cap them off properly.

How should I go about dealing with the waste pipe? It is in a first floor bedroom and, for now, I had just planned to cut it, close to the interior wall, and then deal with the remaining pipework later.

Outside it runs down to a open pipe, shared with a drainpipe, which then runs to the ground and then the main drain a couple of meters away.

I just want the pipe cut so that I can get the sink out of the way.

The waste pipe is metal, not sure what type.

If I cut it, what should I use, and do I need to cap it off, or sever the external pipe to prevent any return of gas? (not sure if that is a problem as the pipework is open where the external pipe meets the drainpipe)

Any thoughts would be much appreciated.

It's copper, use a hacksaw and no need to cap.

Personally, I would remove it, or you may get a pong coming back into the room from the hopper/downpipe/gulley.

Get as much out as you can and weigh it in

Without a cap or plug you have a route for mice until such time as you remove it entirely. Any solid material will do, simply pushed into the pipe.
I'd also cut away as much as possible of the external pipe

Cut it flush with the wall both sides and then fill the hole with a suitable filler/mortar.