Surely I would do better to trust a National fitting company, like Anglian, Everest Zenith or BAC?

A: The large nationals generally have lots of badges to prove their products are tested, but surprisingly not many make their own sliding sash windows. Even some of them choose to buy in sash windows because of the demanding manufacturing tolerances… and remember their sales people probably don't even know their company policy is to buy them in! Some do make sash windows, but because they are sold in such small quantities, little or no investment is made in improving their products, its just not worth their while.

However, at Bygone Windows, Double Glazed Sash windows are our livelihood, so whenever an idea is created, or an improvement is thought of, it's developed and becomes a standard feature of the product, that's why we have over 15 unique inventions on the Bygone Collection of sash windows.