So, Greg
You have his name.
Do you know roughly how old he was/now is?
You could look to see if you can find his birth reference on
www.freebmd.org.ukWere your parents ever married? If so, you could look for their marriage on the same site.
Do you have your birth certificate, and is he named on that?
Once you have more details about him, you can then try to see if he married after he and your mum split up, and if so if there were other children, and then you will have more names to look for on social media, 192.com and so on.
Do look at the link that Sarah posted yesterday, if you've not yet done so.