I was adopted, how would I contact biological parents?

okay so I am 22 now and my mum told me when I was like 3 that I was adopted! I live in Ireland now, but I was adopted in London so presume biological parents are there? A couple of years ago I got a letter looking for contact but I vetoed it, well my mum vetoed it and I just went along with it because I didn't want to annoy her and I just wasn't able to handle it all! It still feels weird to me that I have a mum all my life, but somewhere there are biological parents and family, it just weirds me out, what should I do?