Comment

Understanding Heritage Impact Assessments for World Heritage Sites – A process, not just a report

Historic England’s Advice Note on the Management of World Heritage Sites (WHS) is expected to be released for public consultation this year. The note is due to provide clarity on the application of the current UNESCO guidance in an English setting. Ahead of its publication, our Heritage, Townscape and Landscape team explain the current UNESCO guidance and its practical application for Heritage Impact Assessments (HIA).

The guidance

In 2022, UNESCO published new guidance for assessing the impact of development on the Outstanding Universal Value (OUV) of World Heritage Sites (WHS) replacing the ICOMOS Guidance, which previously provided a methodology for such assessment. The UNESCO guidance is written to be applicable to a huge diversity of WHS across the globe be they cultural, natural or mixed.

One thing for practitioners to be wary of is that this guidance has not been written with the specifics of the UK planning system in mind, which needs to be carefully considered and managed when assessing projects within WHS; either as the applicant or as the determining authority. Historic England is developing a new Advice Note (HEAN) that is due to be published this year, which should provide further guidance on the application of the UNSECO guidance in the English context. The other UK national heritage bodies are expected to follow.  

Why and when are Heritage Impact Assessments needed?

The purpose of undertaking a Heritage Impact Assessment (HIA) is to identify potential impacts on OUV, which is defined by UNESCO as cultural and or natural significance, which is so exceptional as to transcend national boundaries and to be of common importance for present and future generations of all humanity. To be deemed of OUV, a WHS must also meet the conditions of integrity and / or authenticity and must have an adequate protection and management system to ensure its safeguarding.  

Impacts on OUV are required to be assessed at an early stage to ensure appropriate steps are taken to avoid or minimise potential adverse impacts, whilst maximising any beneficial effects. It is a process that shares similarities with Environmental Impact Assessments (EIA) in that it includes scoping and screening stages but which would, if required, be undertaken in tandem as a process separate to planning decision-making.  

Given the exceptional significance of WHS, there is an expectation from the relevant international heritage bodies that any adverse effects (harm) will be avoided and / or demonstrate that an alternative option would not cause less harm. The process of HIA is ongoing through design development and is not simply a report that forms part of the final submission documents for a planning application. The HIA report documents this process and may draw on additional expertise beyond heritage, as relevant to the specific OUV of a WHS and the proposed development. This could include archaeological, architectural, engineering, geological or drainage specialisms. A HIA that accords with the UNESCO guidance will be a requirement for development that has potential to impact OUV.  

The process

Under paragraph 172 of the Operational Guidelines^[1], the UNESCO World Heritage Committee asks to be informed of the State Party's (i.e. the relevant Government department) intention to undertake or authorise major restorations or new constructions, which may affect the OUV of a WHS as soon as possible and before making any decisions that would be difficult to reverse. The purpose of notification is to enable the committee to assist in seeking appropriate solutions to ensure that the OUV of the property will be fully preserved.  

The Department for Culture, Media and Sport (DCMS) is ultimately responsible for the decision on whether a case will be notified to the World Heritage Committee, having taken advice from their technical advisers (Historic England International Team and the relevant national heritage body).

Historic England advises early engagement with the relevant national heritage body(ies) about any potential proposal, since they act as the main conduits for liaison with the State Party. The State Party can then provide preliminary advice and guidance regarding whether a potential development or restoration proposal (or policy document) might need to be considered for notification. The State Party advocates for notification at pre-application stage wherever possible to maximise notice given to the committee and enable constructive consultation.  

This body warns that leaving notification to a late stage increases the risk for all parties that any concerns raised by the Advisory Bodies may then be difficult to address. For example, the World Heritage Committee may require a technical review of the proposed development to be undertaken, which can take several months, and so impact a project’s programme.

Informed by our experience of working on projects with applicants and other stakeholders in WHS over recent years, we endorse this advice as a way to de-risk development proposals. We have found that best results for a project, and ultimately the delivery of planning approval, have come through an approach that embeds the HIA process in that project from the start, and also involve engagement with stakeholders at the right time.  

Challenges and controversy

UNESCO's World Heritage programme is not immune to challenge, even controversy. For instance, the issues of the impacts of global tourism on such historic places and their local communities often feature in the media. The effectiveness and approach of this international body in achieving its ambitious conservation objectives has also been questioned, such as due to its financial constraints or the ability to enforce action where WHS are deemed to be in danger. This is relevant to the UK too and for our planning system and development industry.  

In 2024, two new sites in the UK were added to the World Heritage List: the Flow Country in Scotland and the Moravian Church Settlements (Gracehill) in Northern Ireland. The UK’s current Tentative List includes other sites canvassing to join this exclusive heritage club, such as the City of York, which has gained much press recently.  

Conversely, in 2021 UNESCO removed Liverpool: Maritime Mercantile City from the World Heritage List, citing the destruction of its OUV as a result of new development within its docks. More recently, the City of London Corporation's emerging new City Plan 2040, and its latest growth objectives for office development and tall buildings in the Square Mile, have been seen by both UNESCO and Historic England as a potential threat to the status of The Tower of London WHS.

Needless to say, there will remain a high-level of scrutiny exercised by these heritage bodies and other stakeholders on development within WHS and their settings in the UK. Accordingly, the value of experienced and expert advice for both applicants and planning authorities is critical to ensure the success of development projects affecting these heritage assets of the highest significance.  

All eyes are now on the release of the new Historic England Advice Note on the Management of WHS. Public consultation is understood to be programmed for this year, so do not miss the opportunity to contribute to that process. It will be interesting to see how the Government’s growth agenda, and its narrative on addressing perceived constraints in the planning system that restrict the delivery of new development, is reconciled with that guidance.

How can we help?

Our Heritage, Townscape and Landscape team has developed valuable experience and specialist expertise through working with several clients and project teams through the HIA process, including navigating the referral of projects to the World Heritage Centre for review.  

A window into our track record on advising clients through the HIA process is available below:

• Bath Rugby Club, City of Bath / Great Spas of Europe
• Devonport House, Maritime Greenwich
• The India Buildings and Cowgate, Edinburgh Old and New Towns  

For further information, please contact Richard Brookes, Kerrie Melrose or Hannah Tweedie. 

22 May 2025

[1] UNESCO (2024) The Operational Guidelines for the Implementation of the World Heritage Convention