I eventually found out (following re-evaluation) from the Head of HR the following:
When applying the score to the bands under AfC, if the score is in the lower half of the band, then the evaluation team will re-look at the matching and re-score in order to place it in the next band down!!!!! In other words, you have to score in the top half of the band to be placed in that band."

To match an AFC job description for banding, two sections ‘must be’ matched the Knowledge, training and experience (section 2) and Freedom to Act (section 12), you may then fail to match up to 4 of the other sections and as long as you reach the relevant job evaluation score you should get the band.

When (if) the regulation of Clinical Technologists happens anyone wishing to work as a medical engineer etc will either need to be "grand parented" on to the register or have completed an approved degree.

The AFC description for a Medical Engineering Technician band 5 Section 2:- Knowledge, Training and Experience says "Expertise within specialism, underpinned by theory. Professional electronics knowledge to degree equivalent level, acquired through BEng in electronics or HND + short courses or equivalent training and experience."

So combining the up coming regulation and AFC description it could be argued that anyone coming in to this role requires a degree and that anybody already in this role must have the equivalent training and experience.

As for autonomy unless the person you answer to supervises every thing you do including repairs on wards and work whilst on call then one could argue that a band 5 should be the minimum, for anybody already in post.

The AFC description for a Medical Engineering Technician Specialist adds specialist training and experience to section 2 and is lead practitioner for specialist equipment to section 12, therefore many people may be able to match a band 6.