If your main scheme is a Defined Contribution arrangement, then the Employer must contribute a minimum of 10% of the total contribution for you.
If your main scheme is a Defined Benefit arrangement, then it is more likely that the benefit limit rules will apply.
In relation to Share Options, they are strictly pensionable. So if you are in a DC scheme then in the year you exercise the options you could invest the appropraite % as an AVC. If you are in a BD scheme, its more complicated as it will depend whether the value of the options will fall into the definition of Final Salary for benefit calculation purposes. For example, if the option is exercised in the 10 years immediately before you retire, then the value may possibly be capable of inclusion in the average salary definition for calculating the pension benefit. But if you exercise the option say at age 50 and retire at age 65, then the value will not be included in the final salary computation. You could still invest the % of the option value in the year of exercise, but it potentially brings you closer to the Revenue benefit limits.
I suggest you consult your scheme Trustees or scheme adviser.