Currently grandparents face a two stage process, first applying to court for the right to make an application, and then going through the formal process of applying for child arrangement orders. (vardags.com)
In the meantime please note that any residence orders have now been replaced by child arrangements orders which have the same effect. (frg.org.uk)
The exception is if there is a residence order in place in your favour or child arrangement order confirming that the children live with you. (pannone.com)