No national standards body, such as the BSI, is allowed to change a word of the final approved draft of the Eurocode. However, CEN acknowledges that member countries have the absolute right to determine the level of safety they find acceptable.
There are also factors linked to climatic conditions and local construction practice that are not amenable to harmonisation.
So each member state is allowed to choose what are known as Nationally Determined Parameters (NDPs). These are detailed in the National Annex, which may also include 'non-contradictory complimentary information' (NCCI).
In practice in the UK, NCCI will largely consist of fragments of existing British Standards covering aspects not included in the new Eurocode (see main story) and relevant guidance from authoritative industry bodies.