Written guidance can contribute to the development of effective SEA, delivering relevant information for those involved in policy, plan and programme making processes. Generally speaking, guidance should aim at setting best practice standards. However, to date, how guidance is impacting on SEA effectiveness and how it is best developed and maintained has not been explored to any great extent. As a consequence, it has remained unclear how a key ingredient of effective SEA, namely the support of an enabling context, should be approached. In this paper, we look at the perceived relevance of written guidance for the delivery of effective SEA, based on a two-stage survey with 26 practitioners (all with over 10 years of experience) from the UK and the Republic of Ireland, conducted between 2015 and 2017. Survey participants included representatives of the regulatory, consultancy and academic sectors. Our findings indicate that guidance can promote SEA effectiveness if it: (a) aims to go beyond basic legislative requirements; (b) is able to respond to the specific situation of application; (c) can establish a minimum standard for SEA; and (d) is able to stimulate the advancement of quality standards within a tiered approach to SEA.