The present UK distribution network planning standard, Engineering Recommendation P.2/6 (P2/6), defines the acceptable durations of supply outages following first and second circuit outage conditions as function of group demand. In addition, P2/6 specifies a capacity value for distributed generation (DG) to be used in future circuit capacity planning. The approach does not consider other elements of the distribution network. This paper analyses the reliability performance of distribution system when DSR is used to defer network upgrades driven by load growth. The analysis uses actual DSR performance data from trials that were executed as part of the Low Carbon London project. The DSR contribution to security of supply is assessed using a probabilistic risk modelling framework to further inform a number of topics (i) reliability contribution of DSR technologies in a network context, (ii) strengths and weaknesses of P2/6 in estimating contribution to security of supply, (iii) benefits of contractual redundancy, (iv) impact of DSR coincidence in delivery (common mode failures) on contribution to security, and (v) impact of DSR scale and magnitude on contribution to security of supply.