The European Union funded Horizon 2020 project CLONETS (Clock Network Services) is motivated by recent progress in time and frequency metrology. Novel applications in fundamental physics, geodesy, telecommunication, industry and society require reference signals with significantly higher performance than is currently offered by satellite techniques. Time and frequency transfer methods based on optical fibre links have evolved rapidly in recent years, and are attractive both for very high-performance applications such as optical clock comparisons, and for many industrial applications, as an alternative and complement to radio- and satellite-based methods. However, widespread utilization of such signals require a reliable optical fibre network infrastructure and the high cost of optical fibre rental can be a challenge to the sustainability of these links. Such optical fibre links for time and frequency are being actively developed and operated by several countries in Europe, including some cross-border links. CLONETS aims to prepare the conditions in which these links may be combined and completed to form a pan-European optical fibre network, with a sustainable organisation allowing it to operate over the long term for both research infrastructures requiring high performance links, as well supporting time and frequency services for industry and society.