Mother won't let me see grandson

My son had a fling with a girl, she got pregnant but left the country & refused to have anything to do with him. Eventually she had a little boy, my son asked for a paternity test, which proved he was the father.
They came to England & we all got along well. Then they had a disagreement about maintenance, he wanted to set up an account for her & put regular payments in it. She wanted him to buy nappies & food.
They eventually agreed to try it a month each way then discuss again.
3 days later she contacted me to say she didn't want either one of us near her son.
My question is, do I have any rights?
My son is getting legal advice, but we are scared she will leave the country.