It seems accepted that in a democracy, politicians and public officials have to comply with minimum standards of policy-making - they cannot just make arbitrary decisions.

Some guidance documents are as follows.

In 2001, the Centre for Management and Policy Studies (a section of the UK Cabinet Office) published a document Better Policy-Making [1]. This was based on a survey of senior civil servants reported by the UK Cabinet Office in 1999 [2].

In 2001 the UK National Audit Office published its report Modern Policy-Making: Ensuring Policies Deliver Value for Money [3]. This included (p 32) assessment of four departmental case studies against nine criteria.

A Practical Guide to Policy Making in Northern Ireland was published in around 2002 by the Office of the First Minister and Deputy First Minister [4]

In April 2011, the Institute for Government (a UK charity) published Policy Making in the Real World [5]. According to its website, "The Institute for Government is an independent charity with cross-party and Whitehall governance working to increase government effectiveness. We work with all the main political parties at Westminster and with senior civil servants in Whitehall. We provide evidence based advice that draws on best practice from around the world."

In May 2011, the Institute for Government published The Challenge of being a Minister: Summary and recommendations paper [6]. There is also a longer document.

In June 2012, the Institute for Government published Civil service reform: our verdict [7].
It included a 5-point colour-coded rating scale.

In July 2012, the Institute for Government published Opening up policy making - A case study of the National Planning Policy Framework and other models of more open policy making [8].

In September 2012, the Institute for Government published Evidence and evaluation in policy making - A problem of supply or demand? [9].

References

[1] Better Policy-Making (2001) Cabinet Office, London http://www.civilservant.org.uk/betterpolicymaking.pdf
[2] Professional Policy Making for the Twenty-First Century (1999) Cabinet Office, London http://www.civilservant.org.uk/profpolicymaking.pdf
[3] Modern Policy-Making: Ensuring Policies Deliver Value for Money (2001) National Audit Office, UK www.nao.org.uk/wp-content/uploads/2001/11/0102289.pdf
[4] A Practical Guide to Policy Making in Northern Ireland (around 2002 - the document is not dated) The Office of the First Minister and Deputy First Minister www.ofmdfmni.gov.uk/practical-guide-policy-making.pdf
[5] The Institute for Government (2011) Policy Making in the Real World www.instituteforgovernment.org.uk/sites/default/files/publications/Policy making in the real world.pdf
[6] Institute for Government (2011) The Challenge of being a Minister: Summary and recommendations paper http://www.instituteforgovernment.org.uk/publications/challenge-being-minister-summary
[7] Institute for Government (2012) Civil service reform: our verdict http://www.instituteforgovernment.org.uk/sites/default/files/publications/civil_service_reform_plan_v2%20%282%29_0.pdf
[8] Institute for Government (2012) Opening up policy making - A case study of the National Planning Policy Framework and other models of more open policy making http://www.instituteforgovernment.org.uk/publications/opening-policy-making
[9] Institute for Government (2012) Evidence and evaluation in policy making - A problem of supply or demand? http://www.instituteforgovernment.org.uk/publications/evidence-and-evaluation-policy-making