Pruning of trees is infinitely more complex and skill dependent than almost anyone, including most self professed arborists realises. Work standards within the United Kingdom are controlled in the first instance by the governmental National Occupation Standards, which require that works in any trade are carried out to acceptable standards.
In order to prune trees to an acceptable standard and avoid the type of arboricultural destruction that I witness on a daily basis, arborists require extensive formal training and ideally extended professional mentoring.
Bristish Standard 3998:2010 Tree Work Recommendations, takes the form of guidance and recommendations in respect of all tree work operations. It does provide useful guidance but does not claim to be nor is it a specification. The standard identifies that the 'execution of its provisions will be entrusted to appropriately qualified and experienced people. For whose use it has been produced. Additional guidance is provided by the American National Standards Institution A.300 guide with associated best management practice notes and closer to home the European Arboricultural Council Tree Pruning Guide.
There are no standard pruning methodologies. Each and every operation relies on assessment and evaluation by a competent and qualified arborist. An arborist of good standing will provide ethical recommendations that will fulfil the requirements of the client whilst causing as little harm to the tree(s) as possible.
Clients should never instruct a tree works company without first receiving a written quotation (not estimate), and checking both their insurance level and cover provided and that the operators are adequately qualified to do the works.