These are usually but not always major developments. Information can be found in The Town and Country Planning (Environmental Impact Assessment) Regulations 2017 (Schedules 1 and 2 type development)
The EIA regulations define two different types of developments, set out in two Schedules to the regulations. For Schedule 1 projects an EIA must always be carried out. For Schedule 2 projects an EIA must be carried out if the development is likely to have a significant impact on the environment by virtue of its nature, size or location.
For more information on Environmental Impact Assessments see: