The paper presents a risk-based distribution network planning procedure to perform a comparison (in terms of costs and associated residual risks) among conventional planning solutions and the exploitation of flexibility purchased from distributed energy resources through bilateral contracts or local markets. The procedure has been integrated within software developed by the Authors in the past decades for distribution network expansion planning. The software already includes many of the main distinctive characteristics for a modern planning tool, such as abandoning the traditional worst-case approach, resorting to non-network planning options, and implementing the stochastic network assessment to consider generation and demand uncertainties. Since many flexibility resources are connected to the low voltage system, both medium voltage and low voltage networks have to be jointly analysed to account for their mutual interactions. The planning process has been applied to distribution networks representative of the Italian distribution system. The low voltage system has been represented by replicating few real networks provided by the leading Italian Distribution System Operator. Consumption and generation patterns have been modelled from real anonymised measurements.