On a large project an Arborist would have probably been appointed to carry our a tree survey, so it’s basically their responsibility to find out about TPO trees on the site and include this information in the arboricultural report.

If a tree survey has not yet prepared, the Landscape Architect would normally contact the Local Planning Authority, find out who the tree officer is and send a plan with the site boundary shown asking for info of any trees with TPOs within that site.

Generally, when you do a site visit and you see mature/veteran trees, it’s a hint that a TPO might be in place and you should definitely investigate it.