The National Forest Inventory Forest Research, part of the Forestry Commission, gathers data on the number of trees within woodland in Britain. In addition it monitors the canopy area of trees outside of woodland within. More details of the work carried out and information it publishes can be found here: https://www.forestresearch.gov.uk/tools-and-resources/national-forest-inventory/about-the-nfi/
All woodland is protected against unauthorised removal through the control of tree felling in the Forestry Act 1967, the Environmental Impact Assessment (Forestry) Regulations and the planning system. Activities authorised and supported by the Forestry Commission, including woodland management which has grant support available through Countryside Stewardship and Felling Licences applications, are expected to meet the UK Forestry Standard, the Government’s approach to sustainable forestry.