In most cases retaining walls will not need a development application if the wall height is proposed to be less than one metre in height, it is set back from any boundary and is stepped or terraced so that landscaping can be planted to soften visual impact. However, you should always check with your local council before you start.

More info can be found on the following council websites

** Keep in mind if you construct your retaining wall without obtaining building approval in some cases you may face heavy penalties for committing an offence against the Building Act 1975 and consequently the Integrated Planning Act 1997 ***