The World Heritage Convention is the most popular Unesco heritage treaty. With 186 member states, there are now a total of 878 World Heritage Sites in 145 countries.

The UK, a member since 1984, has 27 - 17 of which are in England. These range from great archaeological monuments such as Hadrian's Wall to industrial sites and landscapes such as Cornish mines.

The sites are subject to all the normal pressures of development and the modern world. The impact of tall buildings has been a particular concern, with Unesco missions to four UK sites since 2006.

Despite this, there is still enormous pressure for places to become World Heritage Sites, either for reasons of prestige or civic pride, or because World Heritage status is seen as bringing sustainable economic regeneration.

But a study by PricewaterhouseCoopers has demonstrated that there is no automatic link between inscription on the World Heritage list and economic benefit - and that there can be significant costs.

Worldwide, the Unesco World Heritage Committee, the governing body of the convention, is concerned about pressures on existing sites, including the impact of development on urban sites. The committee is also concerned by the imbalance of World Heritage Sites between Europe and other parts of the world and the over-representation of certain types of (mostly European) heritage.

There must be concerns about the extent to which continuing growth in the number of designated sites, the resourcing of a system that has not kept pace with this rise and the matching of international concerns with economic needs and national approaches to conservation can be regarded as sustainable.

The number of sites should not continue to grow exponentially and it is time for well-represented western European countries, including the UK, to slow down their rate of nominations or even stop for a time.

If the UK continues to nominate sites (currently the subject of a government policy review), the selection should be focused on gaps in the World Heritage List and they should be of outstanding value to all humanity.

For existing World Heritage Sites, more clarity is needed on Unesco requirements for their management, particularly concerning the impact of development around the sites.

The committee also possibly needs to be concerned more with strategic guidance on the management of sites and less involved in the detail of individual cases. Provided such issues can be dealt with, the system should be sustainable and a source of support for conservation worldwide.

Christopher Young is head of world heritage and international policy at English Heritage.

This article is based on a lecture given last month as part of the Nigel Seeley Memorial Lectures organised by the UCL Centre for Sustainable Heritage. The views are those of the author and not necessarily those of English Heritage