As per ACOP 2014 -

"Workers must have adequate training and experience in the particular work involved to be competent to work safely in a confined space. 

Training standards must be appropriate to the task, and to the individual's roles and responsibilities, so that work can be carried out safely."

"Specific raining for work in confined spaces will depend on an individual's previous experience and the type of work they will be doing. This training will need to cover;

(a) an awareness of the Confined Space Regulations and in particular the need to avoid entry to a confined space, unless it is not reasonably practicable to do so, in accordance with regulation 4 (1);

(b) an understanding of the work to be undertaken, the hazards and the necessary precautions;

(c) an understanding of safe systems of work, with particular reference to 'permits-to-work' where appropriate;

(d) how emergencies arise, the need to follow prepared emergency arrangements, and the dangers of not doing so."