Useful Contact Numbers:
Bristol Family Mediation:
T: 0117 9292002
Families Need Fathers:
Family Rights Group
(Mothers apart from their children)
Jane Jackson Blog
Bristol Grandparents Support
The short answer is in the UK you do NOT have an automatic right to see your grandchildren.
I never advise any grandparent to take the legal route, it is distressing for all concerned, it takes a long time and grandparents have spent their entire savings on legal fees. If you do decide to go to court it is very important that you go to a family lawyer.
If you are successful in obtaining a court order for contact, you need to be mindful that if the resident parent decided not to turn up at the agreed time and place you have to go back to court.