[en] Technical programmes of work managed and undertaken by the UK nuclear power generation industry to develop the R5 high temperature assessment procedures have been ongoing for many years. The development programmes are undertaken by British Energy Generation Limited in collaboration with Serco Assurance. The work programmes have largely been driven by the need to advance the methodologies to enable increasingly complex fitness-for-purpose and plant life extension assessments to be undertaken. This is especially true for plant that has been in operation for a number of years where ageing and material degradation issues are prevalent. The R5 procedures are updated on a regular basis, taking into account the information resulting from the development programmes, and other available information world-wide. This paper provides details of the recent advances in the procedures for assessing creep-fatigue initiation and crack growth in high temperature plant. (author)