Anyone who owns or manages land-containing trees has a legal duty to ensure that they are in a safe condition so that foreseeable damage does not occur due to tree failure. (Occupiers Liability Act 1954/1980). 
Guidance issued by the Government, the Forestry Commission and the Arboricultural Association advises that a tree survey is undertaken by a professional tree surveyor every 2 to 5 years. Failure to do so may leave those responsible liable to prosecution. A tree survey is an essential component of any system that demonstrates responsible land management.

Mortgage lenders may require a tree survey, especially when mature trees are close to buildings. A survey informs the lender what species of trees are on or adjacent to your property and how they can affect your property or your neighbours.  Even when not a condition of the mortgage, a professional survey reduces the risk of buying a house with potentially hazardous or damaging trees that may need works carrying out at your expense.