Is the success of conservation policy dependent on design guides and article 4 restrictions? I need a policy review on conservation areas at National, Regional and local level,

The planning system includes the following parts:
• Legislation (Primary Legislation; Planning (Listed Buildings and Conservation Areas) Act 1990 )
• National Planning Policy and Guidance
(12. Conserving and enhancing the historic environment (National Level) +relevant guidance provided from PPS5)
• Regional Level (London Plan)

Is the success of conservation policy dependent on design guides and article 4 restrictions? I need a policy review on conservation areas at National, Regional and local level,
Historic England Practice Advice (which advices local authorities hat to do to achieve policy objectives set in primary legislation)
• Local Level
-Conservation Are Appraisals
-Supplementary Planning Guidance
Site specific policy for Hampstead Garden Suburban and Watling estate (London Borough of Barnet)

Is the success of conservation policy dependent on design guides and article 4 restrictions? I need a policy review on conservation areas at National, Regional and local level,