INDG32 published by HSQE states:

Employers have a duty to consult with their employees, or their representatives, on health and safety matters. This leaflet is aimed at employers and discusses what they need to do to ensure they are complying with the law.

For clarificaion, if a company has a union and they consult with their employees directly who are affected by the change does that company still have to consult with the Unions?

All depends upon the recognition agreement between employer and union.

In an "effectivley closed shop" all discussion is with the union even on behalf of those employees who are not union members. This would not be the case where one or two employees were members of a union (recognised or not) and the majority of the workforce were not part of that union.

Common courtesy dictates you involve the union where present otherwise you may end up in conflict.

Once had an employer try to use a divide and conquer approach to what were site wide redundancies by talking to small groups individually hoping to avoid the total head count triggering proper consultation.