Carpet fitting on stairs and landing

If you want to fix stair carpet invisibly, put two gripper strips in each concave corner between the tread and the riser - one on the tread and the other on the riser, each about 10mm from the corner, and with the spikes pointing into the corner. Cut the carpet to the right width for the staircase, and bash it into the corners with a blunt bolster chisel. If you have to join it, do so in these concave corners.

No idea about the second question!

Roger

My carpet fitter asked me not to remove the existing carpet from the stairs before he came so he could use it as a template if he was getting short and avoid any waste. In the event, he had enough left when he got to that part and didn't do this, but that's one idea at least. These stairs had a winding (several cheese wedge shared stairs) which took the staircase through

A carpet supplier will be able to supply cut doormat to exactly the same height as the surrounding carpet and underlay, for exactly this purpose.

You need some form of recess as mats are rather thicker than carpets. Easy enough with a suspended wooden floor although it involves a fair amount of woodwork, but I'd say pretty difficult with a solid floor.