Can you enter a confined space without a confined space permit?

The answer is yes, you can.

According to the regulations, to enter without a confined space permit, workers can choose to wear self-contained breathing apparatus to enter to work. 

There are certain types of works such as tank cleaning works that people have to enter to clean manually, and the toxic gases inside will exceed all safe limits. 

So, there is really no point in doing gas tests and write it down in the permit since all the gas readings will be xxx.

Quoted from Workplace Safety and Health (Confined Spaces) Regulations 2009