If your tree(s) that requires work resides in a conservation area or has been assigned a TPO then you will need to submit a planning application. This can be done by anyone but we would suggest using someone who knows what is required as planning applications are routinely rejected for fairly insignificant reasons. For example a requested crown reduction expressed as a percentage figure (which is an industry standard term) will be rejected unless it is also expressed by the amount in metres which it is to be reduced. There seems to be no other reason for this other than the local councils particular procedural methods.
We can submit this for you for an administrative fee commensurate with the complexity of the application. Normally our fee is around £50-75 but will save you hassle and time.