One can take an ambivalent view of the approved workshop scheme. On the face of it (and it does have the potential)to provide the end user with confidence about the scope of work and the competency of an approved workshop, and to raise standards by raising expectations. But it is also a mechanism to discourage end-users from using none membership businesses.
Just in case any reader is not aware about the actual status of the NCC, I suggest you review the NCC website at:-
http://www.nationalcaravan.co.uk/Default.aspx
You will see it is trade only organisation with no unbiased end-user representatives. (The 'Clubs' are actually businesses with profit motivations)
As it is funded by its member businesses, the NCC is unlikely to take a stance that undermines any of its members, which suggests that in any situation where there is conflict between business and end-user interests, it is more than likely to side with business.
The NCC has no statutory powers to police the industry, Its ultimate sanction is to remove a businesses from its list of members, and thus deprive a business of a voice within the NCC.
Caravan related businesses are not obliged to seek NCC membership, and none membership is not a bar to trading in the industry, however the NCC members will usually prefer to do business with other NCC members.
The NCC is recognised by governments as a legitimate lobbying organisation for the caravan industry. It is also accepted as organisation with access to technical expertise related to caravans, and so it is usually admitted to the working party committee stages that precede green, white and government technical papers affecting the caravan industry and related trades.
With regard to the Approved Workshop Scheme. The scheme is not obligatory it is only voluntary. It carries no legal force, but assuming compliance with the schemes standards is monitored and where found lacking, action is taken, the only sanction the scheme has is to remove the workshop from the approval scheme.
One might hope that standardised documentation and levels of service may be adopted by participating businesses, it is not a legal requirement, so bespoke documentation is still possible.
Fundamentally and not dependant on membership of any trade scheme, any business that sets its self up and advertises its self to undertake work of a nature that requires a specialised technical knowledge or tools, (such as service centres) is legally bound to provide services of a competent and safe nature. Failure to so is a trading standards offence subject to law. With this in mind it raises the question of the need for an approved workshop scheme!
Ultimately any work an end-user asks a business to carry out is subject a contract between the end-user and the business. The NCC has no part in that contract. The terms of the contract should be settled before the work commences, and to that purpose the end-user can ask to see schedule of works such as the 'service sheet' and can clarify the acceptable standards of the work to be carried out. Together, the client and business may agree to adopt and use the Approved Workshop schedule and success criteria.