The provision of Defence support to civil authorities in the UK is governed by through the Military Aid to the Civil Authority (MACA) process which is driven by a robust and well-defined set of principles, set out in a publicly available Joint Doctrine Publication. These are that MACA may be authorised when:
- there is a definite need to act and the tasks our Armed Forces are being asked to perform are clear;
- other options, including mutual aid and commercial alternatives, have been discounted; and
- the civil authority lacks the necessary capability to fulfil the task and it is unreasonable or prohibitively expensive to expect it to develop one; or
- the civil authority has all or some capability, but it may not be available immediately, or to the required scale, and the urgency of the task requires rapid external support from the MOD.