The The Town and Country Planning (Environmental Impact Assessment) (England and Wales) Regulations 1999 apply to any development likely to have significant effects on the environment by virtue of its size, nature or location.

If a Local Authority fails to follow correctly the requirements and procedures set out in the regulations, this can result in planning permission being successfully challenged.

If no EIA is carried out, this can lead to a challenge in the courts.

For example, a decision to grant planning permission to erect residential units, on land contaminated as a result of its former use, was quashed in the High Court on a point of law because the Secretary of State had unlawfully taken proposed remediation measures into account when determining whether an EIA was necessary. It was judged that where an EIA was required, the regulatory scheme required separate information to be provided on the likely environmental effects and measures to reduce or remedy those effects. This decision was then challenged in the Court of Appeal.

The Court of Appeal ruled that while in some cases, where the remediation required would be 'modest in scope', it can be proper to take the proposed measures into account when determining whether an EIA is necessary, this would not be the case where more uncertainties are associated with the remediation measures: in effect, saying that each case must be looked at individually. On the facts of this particular case, the court decided that the Secretary of State could not have properly concluded that the likely environmental effects were such that an EIA was not required.

In the second case, a challenge that it had been unreasonable and unlawful for a Local Authority not to require an EIA was overturned. The High Court held that there was no 'bounding principle' requiring an EIA. Only 'significant' effects would bring a development within the scope of the EIA Regulations. It was for the Local Authority to judge and their decision in this case had been reasonable and lawful.

A recent decision by the court to limit the costs of a protestor who objects to a development near Hampton Court shows that the courts take the environmental aspects of planning decisions seriously and are willing to try to ensure that objectors on environmental grounds are not deterred by the potential costs of taking their challenge to the court.