If you're content that the work method is valid, all reasonably practicable measures are in place, your people have all had and are all following the training, nothing untoward is observed (supervised) or reported, then NO. There are other middle-ground options such as in-house team talks, refreshers etc. For me, refreshers are valid where skills are little-used, e.g. First Aid; or high-hazard tasks, e.g. FLT & plant operators.

Many thanks ron / rob; this would (obviously help us from a cost and logical point of view - we hace 100+ site operatives).

This is worth a read. Research by Loughborough Uni for the HSE back in 2007 http://www.hse.gov.uk/research/rrhtm/rr583.htm "The results of the systematic review indicate that there is little evidence supporting the effectiveness of technique and educational based manual handling training. There was considerable evidence that principles learnt during training are not applied in the working environment, i.e. there is little transfer of training from the learning environment to the working environment."

No requirement for MH referesher training at 3yr periods. Personally - and this will be controversial - I don't think MH training is effective. Not in the traditional context of MH training.