No it is not compulsory to have an actuarial valuation; check the standard 26.18:
If an actuarial valuation has not been prepared at the date of the report of a defined benefit plan, the most recent valuation should be used as a base and the date of the valuation disclosed. The actuarial present value of promised retirement benefits should be based on the benefits promised under the terms of the plan on service rendered to date, using either current salary levels or projected salary levels, with disclosure of the basis used. The effect of any changes in actuarial assumptions that have had a significant effect on the actuarial present value of promised retirement benefits should also be disclosed.
