Prior to carrying out any work on a tree always contact the local authority to ensure that the trees are not protected by a Tree Protection Order, planning constraints or that the tree falls within a conservation area.
Always employ a suitably trained professional tree surgeon, who is covered by public liability insurance, ask for proof.
Never employ house callers or leaflet droppers claiming to be professional tree surgeons.
A reputable tree surgeon will normally send you a written quotation which will give details of the work to be undertaken, their address and qualifications.
Do
inspect your trees regularly;
ask for advice from a reputable tree surgeon if you are concerned about anything;
ask for advice about fungus or cavities;
check for dead or broken branches that may be dangerous if they fall.
carry out unnecessary pruning;
alter the ground level under a tree, including the excavation or building up the ground;