If someone falls off my roof can I be sued?

[RosemaryWoodhouse]

My sweetheart has hired a dodgy looking builder to do some tiling on our roof. They said they were going to put up scaffolding but they haven't done. I'm pretty sure this violates health and safety and I am worried that if one of them falls we can be sued. Who is liable - them for not doing it properly or us for not ensuring it is done properly? I don't like how they look at me either.

i wouldnt know rosemary, my DP is a carpenter

It is down to the building firm to set out & comply with safe systems of work for their employees (ie the blokes on the roof). Certainly now, the Health & Safety Executive is pretty hot on work at height, & if scaffolding isn;t being used they would expect a pretty robust alternative.
As the house holder, if you have concerns about the safety of the workers, I'd contact the HSE or you local council if the company themselves don't appear bothered.

They've come back today and erected scaffolding