What is the official complaints procedure for bailiffs?

None

You cannot make a complaint against a bailiff, unless you have evidence to show that his is unfair to hold an enforcement certificate.^[1][2]

If you want to make a claim against a bailiff, then make a money claim online.^[3]

Do not engage the bailiff company's own complaints procedure, it's designed to wear you down and make you give up your complaint. Only use it if you want to draw out their defence before starting a claim.

Bailiff trade associations represent the interest of bailiffs and their companies.

If you have a complex claim, then start by addressing your claim to the local authority the bailiff represents, and escalate to the Local Government Ombudsman. This can also draw out their defence before starting a claim.^[4]

^{[1] Regulation 9 of the Certification of Enforcement Agents Regulations 2014
[2] See Making a complaint about the bailiff fitness to hold a certificate
[3] Part 27 of the Civil Procedure Rules
[4] See Local Government Ombudsman}