Please don't frighten the OP unnecessarily.
As you were married to the mother of your child, it would be extremely difficult for the step parent to adopt your child without your agreement.
The court can dispense with your agreement but only if there is a VERY good reason. As you have regular contact with the child and have supported him this would be highly unlikely.
The reasons your agreement can be dispensed with are any of the following:
The parent or guardian cannot be found or is incapable of giving agreement;
* The parent or guardian is withholding his agreement unreasonably;
* The parent or guardian has persistently failed without reasonable cause to discharge his parental responsibility for the child;
* The parent or guardian has abandoned or neglected the child;
* The parent or guardian has persistently ill-treated the child or
* The parent or guardian has seriously ill-treated the child.
Regarding name change - have a read of this:
http://www.yourrights.org.uk/cgi-bin/ubb/ultim atebb.cgi?ubb=get_topic;f=19;t=001672