My undergraduate supervisor is giving me very little help I am a  student in my final year of an undergraduate programme. The majority of the credits going towards my degree are weighted on a lab based thesis which is supervised by a very time constrained professor. We are supposed to be working almost all day in the lab under instruction from our supervisor. 
However they are always close to an hour late whenever we are supposed to meet. When they do arrive, they are so rushed they say something small to do and give very little explanation and then leave. There is no structure and the majority of the time I am left without work to do.
The thesis is hugely important to me as I would like a career in the field. 

I don't know how to approach them. I want to start progressing more with my project but it is difficult trying change thing someone who is partially grading my thesis and I am unsure of the best way to go about this.
Any help would be greatly appreciated.
Let me suggest polite collective action. Have a group of you, maybe three, go to the prof during some scheduled time and just present the case that you need more direction and ask them to find a way to provide it. Or alternatively, a way to be a success without it. 

Try to present it as a need, not as a complaint. The prof may also be dissatisfied with the amount of supervision they can give. You are generous in your assessment, and this will help. But the prof does owe you proper supervision under the circumstances you describe.