Same situation on preserved railways. Yes, volunteers are classed as employees for Health and Safety purposes.

Once a vessel is under the command of its master things change. This is a complicated/specialist law area and maritime areas/laws need to be condidered. However before and after the crew [volunteers, PAYE employees and others] become under the masters complete control then all other things apply e.g. HSWA

Ray its an insure lifeboat and it was a grass covered dyke with a sloping banked side 10 feet high.

The lifeboat crew dynamically risk assessed and decided no lines were required as they saw the casualty in trouble. By the way the casualty could see them??????

Fire service threw rank on them and told them to wait until ropes were provided.

Children run up and down and slide down theses banked sides in summer.

What happened to reasonably practicable ?

I volunteer with another organisation which provides specialist support to the blue light services - when we are called out we come under the direction of the agency or service that called us, so if the incident commander says "don't do that", we don't do it. I suspect your inshore lifeboat crew would come under the same rules, although it depends on the pre-existing agreement you have with the fire service.

As to the original question, yes volunteers are employees - however in the case you've described the volunteers are employees of the inshore rescue charity, not of the fire service. As I've already said, there's probably some sort of mutual assistance agreement between the organisations and that may well put the lifeboat people under the direction of the fire service incident commander.

So Paul
You suspect that the official blue light services might go home with their ball and not let the volunteers play anymore...
And so put people at risk as the volunteers provide a service that the official agencies don’t provide...
Someone should write to the Daily Mail about this...