Rent Increase - transferring property to son - HAP tenant

We are transferring a property to my son and he wants to increase the tenant's rent as it has been the same for the last four years. She is a HAP tenant and I understand that she can claim extra money if her rent goes up. I also understand she has to get 90 days notice so I am wondering if we should give that notice now or if our son as the new owner should draw up a new lease. Any advice would be appreciated

Be very careful with what your son is proposing. Not saying he's wrong, but if the tenant stops paying their share of the rent the council will exit the agreement and you're left with nothing coming in at all and you'll find it almost impossible to evict the tenant, not to mention the trouble and cost involved in trying to do so. Then again maybe the rules have changed with HAP tenants recently?