The government decision to change the security readiness level, on the UK mainland, from ‘moderate’ to ‘substantial’ came as a surprise to many, even though some have been warning the 1916 Centenary could be marked by an attack to advance the 'dissident' Republican cause.

RUSI has a very useful commentary:https://rusi.org/commentary/new-ira-may-2016

Within is this curious passage:
Ironically, one of the gravest threats to the New IRA comes, not from the British or Irish security forces, but from Dublin-based criminal networks which have recently assassinated a number of New IRA members.