From 1st July 2013 it became a legal requirement for unit manufacturers and window fabricators to use the CE mark on their products. To use the CE Mark a company must be complying with EN1279 for units and EN14351 for windows. Window fabricators buying units from another source, must ensure that source is complying with EN1279.
To comply with EN1279 you must have the following:
Working as agents for BSI, we can arrange your Part 2 and Part 3 testing. We handle all documentation, collect your units and deliver to BSI on your behalf. We carry out Part 6 periodic testing at our factory in Leigh, Lancashire, covering the whole of the UK.
Most standards are self-compliant. Third party auditing of your company is not necessary and unless this is needed, you are adding unnecessary costs to your business.
The NHBC and some local authorities may insist on third party certification, i.e. a Quality Mark such as Kitemark. This has nothing to do with the standard but you will need to get a Quality Mark to satisfy your customer.