Why does a UK university need to know my sexual orientation and religion? I want to apply to a postdoc position at a UK based University.

They want me to fill a "Equal Opportunities Data" form with questions about my marital status, sexual orientation, religion and race. Why do they need that? Will there be any consequences from not specifying these? 

Will the employing professor have access to the data?
The employing professor will not have access to this data. 
You can omit anything in this form.
The data from this form goes to HR and is aggregated there so they can prove to auditing bodies that the staff distribution is not skewed (i.e. that they are not discriminating on basis of whatever)