The nature of our product means we use temporary walkways / bridges in place at various stages to prevent falls from height during a build process (boat building) Historically we have made these ourselves from wood but we are now getting that little bit more professional and having them made up from aluminium. Do these need to be certificated to a load bearing strength as per mezzanine floors etc. The company who are making them up have asked us if it is something we would like (at considerable cost) along with annual checks of welds etc I can understand the reasoning & it seems a best practice but is it a necessity? As usual any help would be appreciated

T-Bone, taking the broader risk management view, as Darach suggests, may lead you to consider how you would be able to verify that you had provided safe access and a safe working place etc if challenged post-event. Simply saying "it was built from welded metal and looked OK" is likely to lead to some probing follow-up questions and lack of convincing answers. If these structures are for long term use and subsequent reuse then the financial argument becomes less significant.

Forgot also to mention the walkways should be handrailed etc (I would suggest two rails using the scaffold spacing which off the top of my head is about 450mm and 980mm or there abouts) this is to ensure the risk of a person falling is minimized.