If a tree is not protected by a TPO, can I remove it or prune it without constraints?

Trees in a conservation area that are not protected by an Order are protected by the provisions in section 211 of the Town and Country Planning Act 1990. These provisions require people to notify the local planning authority, using a ‘section 211 notice’, 6 weeks before carrying out certain work on such trees, unless an exception applies. The work may go ahead before the end of the 6 week period if the local planning authority gives consent. This notice period gives the authority an opportunity to consider whether to make an Order on the tree.

https://www.gov.uk/guidance/tree-preservation-orders-and-trees-in-conservation-areas

Subject to specified exemptions, a licence may be required for the felling of growing trees

Your nearest Forestry Commission or Natural Resources Wales office will advise whether you require a felling licence.
https://www.gov.uk/guidance/tree-felling-licence-when-you-need-to-apply

Why and how can TPO status change?

Land use might have changed since an order was originally made; land might have been developed; trees might have been removed; trees still standing may no longer merit the protection of the TPO; new trees might merit protection; the TPO map might bear little comparison with a modern map. If you are a landowner, our expertise in the evaluation of the TPOs system can help you to oppose an inappropriate order or provide well-reasoned justifications to remove or prune protected trees

How do I find out whether my trees are protected by a TPO?

Most local planning authorities have an online interactive mapping system that you can integrate. Some are still in the dark-ages and you will need to telephone or email your enquiry. You can obtain copies of tree preservation orders from the local planning authority, but most charge for this service.