[Glosterboy]

September 2021 I sowed for the first time Mustard Green Manure. Can't remember exactly but when the plants were approx couple of feet tall spaded the areas. Therefore turning as much green foliage as possible back into the soil. Hard Work!!!!! Already got my Mustard Green Manure seed for 2022. Done some research since. And discovered the following procedure, before flowers set, cut foliage to ground level and leave to rot on top of soil prior to digging the areas over in early spring. So please what/which is the preferred/best ways and means when dealing with Green Manure? The easier the best after 2021!!!! Thanks.

[New shoot]

I would go with the method you have researched.  The top growth will rot down and be easier to turn in.  The roots will hold air spaces in the soil and keep the structure there long after the tops are cut.