AS you know you are the responder as you respond to the petition, the petitioner is the other side who asks for the divorce by filing a petition.
You will not get legal aid and there will be little point in defending the divorce or cross-petitioning as the grounds are now that the marriage has broken down irretrievably, if one party is claiming this it is difficult for the other to say the marriage still exists.
If you do not defend or cross-petition it will be very straight forward and Cafcass (children and family court advisory & support service) will be brought in if children are involved and you probably will not need a solicitor. Try to agree as much as you can with the other side, you will first be issued with a decree nisi (meaning unless) followed by some 6 weeks later with the decree absolute at which point you are no longer married.