Can your site be developed?
Most people are aware of the need for Planning Permission, but other Statutory permissions may also be required.
The very first thing you may need to check is whether any utility services are running under your site, particularly drainage, as these sometimes have enforced 'no build' zones. These specific issues are not fully identified by Statutory Consultations during the Planning process and remain the developer's responsibility to establish and address. There is a risk that you could be granted successful Planning Permission for land that later cannot be developed due to underlying utility restrictions.
The best starting point can often be to request a domestic 'sewer trace' from the Water Authority to check there are no major sewer pipes that might prevent new development and that a Build-over Sewer Agreement (BoSA) is likely to be possible. DCWW guidance can be found at https://developers.dwrcymru.com/en/applications/planning/building-over-or-near-to-sewers
You could also consider a more comprehensive camera survey by a specialist drainage company, or commissioning an independent 'Utility asset mapping' search by a survey company.
These searches have 'up front' costs associated with them, but can save time and abortive work later on.
Put another way, it is better to try and find out early rather than discover it after site works have commenced.