As Jackdaw33 indicates, grandparents have very few rights in respect of their grandchildren. After all, young people have the right to leave home at 16 and never have any contact at all with their parents from then on, if they so choose. If they then go on to have children of their own, the grandparents of those children consequently won't know (or have the right to know) that they've even got any grandchildren.
However to say that grandparents never have any rights in respect of their grandchildren isn't strictly true. When the parents of children divorce or separate, the grandparents of those children can apply to the court handling the arrangements for the future care of the children to be admitted as parties to those proceedings. Under such circumstances a court might award visitation rights to the grandparents but it's certainly not guaranteed.
That doesn't usually help though when the parents of the children haven't divorced or separated, as it's unlikely that a court would make a Child Arrangements Order in respect of a child who's living with both parents. (The appication process for a Child Arrangements Order isn't straightforward either. It's necessary to first attend a Mediation Information and Assessment Meeting before seeking permission to apply for a Child Arrangements Order, which isn't automatically granted).