Depending on the renovation plans you ultimately go you, you may need to anticipate regulatory or administrative difficulties of varying proportions. Extensions are the biggest possible intervention you can make
on a property, and investing in a property survey beforehand can be invaluable to ensuring your build is possible in that regard, let alone wise.
Some housing areas are under Article 4 direction, which means even renovations not usually subject to planning permission approval
can require local authority permission
This is before even considering the necessity of any renovation works to comply with national building regulations.