Well, the idea that it doesn't matter whether you are separated or divorced might be a British thing. I don't know. I know there's a clear difference where we live.
What I mean is, go and check out the laws regarding divorce in the country you and your husband have been living in. It's often possible to get that country's laws applied to a divorce since both of you still have ties to the country (I.e. property). This might be easier than trying to divorce him using UK law. However, yes, you need a solicitor. Preferably an experienced one, who knows what they are talking about. You could also employ a local solicitor.
If your husband isn't playing ball, then just complaining won't cut it. Yes, a solicitor costs money, but you'd most likely end up with half the equity of the house and a solid child maintenance agreement.
We are in the EU. We are divorcing according to the laws here, since both of us still live here. I've never tried to have "free" sessions with a solicitor. I don't think that's a thing here. I have a solicitor, who is experienced and specialises in family law, though. I'm fully expecting a huge bill at the end of this. However, if I didn't earn well, I could apply for financial aid. Again, check the rules in the country your husband still resides in. This might be an option for you if you go down that route.
I knew about the possibility to have my ex prosecuted for non-payment of child support (even if he went back to the UK) by reading up on it online before I even saw my solicitor. However, I'm in a country where the government would advance the child support and then get it back from the non-paying parent, if I really couldn't sort it myself.