There is no automatic right in England & Wales for grandparents to see their grandchildren or to have any involvement in their upbringing. However, the Courts are beginning to recognise the often invaluable role that grandparents can play both in bringing up children and supporting separated parents. It is very rare that a Court would deny the grandparent access unless there is evidence of the child being placed at risk of harm.
As grandparents do not have parental responsibility for their grandchildren, they must first ask the Court for permission to bring an application. In order to be awarded such permission, the judge will consider the relationship between the grandparents and the child, the nature and motivation of the application and whether the application may harm the child in anyway. If permission is granted then the application continues in a very similar manner to that of a parent and ultimately, if you and the parents are unable to reach agreement as to how and when you should see your grandchildren, a judge will make this determination after hearing all of the evidence.
If you are or become the main carer for your grandchildren, you do not acquire any legal rights by circumstance and you will still need an order from the Court to confirm the arrangements and also to enable you to legally make decisions on behalf of the child for things such as education, health or religion. It may also be worth considering making an application for a Special Guardianship Order as this gives you the ability to make decisions for children without the need to obtain the consent of their parents who will have retained parental responsibility.