The power to make secondary legislation is set out by primary legislation. As primary legislation sets out legal framework while secondary legislation sets out detailed rules and procedures.
Devolved assemblies/parliaments have different areas over which they can make primary legislation.
"Success":
Has not led to the break up of the UK
Elected mayors have led to greater regional identity in England
Has secured a peaceful environment in NI for 20 years
Devolved assemblies are very popular, no main party's lobby against it - wales has increased demand for greater powers
"Failure":
England has been short-changed in the devolution settlement -failed to resolve West Lothian question
Scottish parliament has increased desire for independence
Public interest in devolved assemblies is low, low turnout
Complex, different policies were necessary to support different devolved regions
Policing is devolved in Northern Ireland and Scotland but reserved in Wales. Devolution in the UK is therefore characterised by asymmetry that continues to evolve, which means each of the three devolution settlements involve varying areas and levels of power.