Hello and thanks for trusting me to help you today. I am a licensed diagnostic and repair technician, I look forward to working with you.
It is normal for the engine rpm to be limited when stationary. This is due to the emissions to keep the engine within its limits. When a smoke test is carried out for the MOT, rather than being revved to the red line, it is limited to keep the engine within its emission range. This helps keep it in a lower tax category.
Yes it is a bit worrying for some people but providing it revs to the red line with full power delivery once moving, there should be nothing to worry about.