(Quoted from the HSA site) The Safety, Health and Welfare at Work (Confined Spaces) Regulations 2001 cover all work in relation to confined spaces.
Regulation 5 states that:
A person shall not carry out work in Confined Spaces if it is reasonably practical that it could be avoided
If the work must be carried out Hazard Identification and Risk Assessment must be carried out prior to the work commencing
A person shall not enter a confined space unless there is a system of work in place that has been planned, organised, performed and maintained so as to render that work safe and without risk to health
Anyone entering a confined space must be provided with appropriate information, training and instruction appropriate to the particular characteristics of the proposed work activities.