If the wall is between 2 private pieces of ground, i.e, yours and your
neighbours land then it can be up to 2 metres high. If it borders onto the
highway (this includes footpaths and public right of way areas such as
grassed areas and common land then it can only be 1 metre high. If though it
is between yours and your neighbours but borders onto a public
access/highway then the area onto the public section can only be 1 metre
high so a front garden wall will for some of its length at least require
permission for it to be over 1 metre. Speak to your local planning/building
control to check accurately what is required