Historic England's reassessment of the mausoleum, following a request by Broadland District Council, has revealed a range of previously unrecognised features that demonstrate its national significance, and resulting in its listing being amended and elevated from Grade II to Grade II*.

The Trafford Mausoleum, located in the churchyard of St Mary's Church, was first listed in 1984. However, the original list entry had not been updated since and did not fully capture the building's architectural, historic and religious significance.

New evidence highlights the mausoleum as the first completed ecclesiastical commission of renowned architect Anthony Salvin, whose later work would play a major role in shaping church architecture and the Gothic Revival movement in England. The building is also recognised as an early and highly disciplined example of the Early English Gothic style, created just a decade after Thomas Rickman's pioneering work defining Gothic architectural forms.

The reassessment also highlighted the mausoleum's rarity as a significant example of Georgian funeral architecture. Unlike most monuments of its period, which followed Classical architectural traditions, the Trafford Mausoleum adopted Gothic forms and was commissioned by a Catholic patron in a highly visible public setting.

The review also included a detailed examination of the building's interior, which had not previously been fully assessed. Researchers found an exceptionally rich scheme of decoration that surpasses the already impressive exterior. Features include intricate dogtooth mouldings, painted and gilded roof bosses, stained glass windows, memorial plaques, heraldic detailing and finely carved stiff-leaf capitals.

Despite minor alterations over time, including the closure of the burial vault and installation of a permanent altar above the former access point, the building remains remarkably intact and retains its outstanding architectural character.

In its recommendation, Historic England states that the Trafford Mausoleum possesses "more than special interest" and therefore merits upgrading to Grade II*, a designation reserved for particularly important buildings of more than special national significance.