https://brexitfacts.blog.gov.uk/2019/09/12/yellowhammer-factsheet/

Yellowhammer Factsheet

The Government has published its response to the humble address motion passed by the House of Commons on 9 September. The below fact sheet contains key points regarding the publication of the Operation Yellowhammer: HMG Reasonable Worst Case Planning Assumptions document. 

What is Yellowhammer? Why is it called Yellowhammer? 

Operation Yellowhammer is a cross government programme of work to ensure that Government is prepared to mitigate the potential reasonable worst case scenario impacts of Brexit if the UK leaves the EU without a deal. 

Operation Yellowhammer is coordinated by the Civil Contingencies Secretariat. The Civil Contingencies Secretariat are part of the team looking at Brexit preparedness, in addition to their regular work building the UK’s resilience by coordinating cross-government preparations and responses.

The government regularly uses randomly selected names for programmes and operations.

Is Yellowhammer a recent development?

Operation Yellowhammer has been in existence for over a year. As the NAO reported in March, the Civil Contingencies Secretariat (CCS) began work on government’s contingency preparations for a no deal exit in June 2018. 

The NAO report also made clear that in Operation Yellowhammer “Departments are working on the basis of a reasonable worst case scenario.”

What are planning assumptions?

It is standard practice for government to use “planning assumptions” when developing contingency plans. They are not a prediction of what is going to happen, but reflect a responsible Government preparing for reasonable worst-case scenarios. Reasonable worst case planning assumptions provide a common, stretching, scenario for stakeholders to plan against and for which, if plans are in place, a reasonable level of preparedness can be expected for most manifestations of the risk.

This methodology is used by governments and organisations around the world as good risk management practice. In the UK reasonable worst case assumptions provide the basis for all national and local risk planning, as set out in the UK’s National Risk Register.

How are the planning assumptions developed?

Officials in departments across government, with the support of specialists and industry, have developed the planning assumptions through rigorous analysis and challenge. Planning assumptions can change over time as new evidence emerges.

Is Yellowhammer a base scenario or a reasonable worst case scenario?

Yellowhammer has always been a reasonable worst case scenario and never a ‘base’ or ‘central’ scenario. This was confirmed in the NAO report, published in March 2019, which said that in Operation Yellowhammer “Departments are working on the basis of a reasonable worst case scenario.”

What does ‘base scenario’ mean? How does this compare to ‘worst case’ scenario?

Some iterations of the Yellowhammer assumptions have used the phrase ‘base scenario’ to describe some baseline parameters - such as the UK will leave on a particular date and be treated as a third country by the EU - upon which the reasonable worst case assumptions are then built. This has never meant that Yellowhammer is a base or central scenario and to suggest otherwise is wrong.

But the Scottish Government say the Yellowhammer document they received was a “base scenario”

Yellowhammer has always been working to a reasonable worst case scenario. The Scottish Government has received an explainer alongside the yellowhammer document which states: 'A planning assumption is: The reasonable worst case scenario you are anticipating, including the likely severity and duration. A reasonable worst case scenario is the worst plausible, not most likely, manifestation of the risk in question.'

How likely is the Yellowhammer scenario?

It is not a likely scenario or a prediction but an outline of what could feasibly happen in a reasonable worst case. The assumptions are deliberately stretching and challenging in order to facilitate effective contingency planning.

Which version of the Yellowhammer assumptions have you published?

We are currently updating the assumptions (as happens regularly) for Operation Yellowhammer but in light of the motion brought forward by the Rt Hon Dominic Grieve MP that was passed in the House of Commons on 9 September, the Government has published the most recent complete iteration of the Operation Yellowhammer document, which is largely based on assumptions drawn up under the last Government. We have redacted one section of the document  on the basis of its commercial sensitivity.

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