Convince Parents to let me Volunteer Abroad...?

Im taking a gap year because I don't think im ready to go to university yet! I feel like I still need to figure things out with myself and its been only a few days into my time off and im already feeling useless... just laying around the house bored. I have been wanting to go Volunteer Abroad in the England for the past year, ever since I went their last summer to visit my family. Problem is ... I don't know how to convince my parents.. I thought I could show them im a responsible person and everything and they would agree... but talking to my sister today she said they would probably say no cause their Pakistani Parents. I said to her we have family their but shes like they wouldn't let me go especially because of family drama. I really want to go like the cost and everything isn't the problem, my parents are the only problem ! How do I convince them ??? Thanks :)