Oh mrscolleydog that's awful. Been there too, 10 months in our case for a very straightforward adoption. It can be so stressful and so confusing for the children if they're old enough to understand.
I agree completely with donquix, chase up, do as much as you can by email and cc all parties into relevant communications in order that you have a clear record. Get the IRO to try and push them. If things still don't move tell them 'we're not making a formal complaint at this point, however if we don't get satisfactory responses we will have no choice.'
We're still in dispute with our local authority with regard to unnecessary drift and delay in our adoption 12 months after the making of the AO. You can't make them undo the damage that has already been done but the more adopters complain and challenge this kind of crap practice maybe the more they'll pay attention. Everyone knows how strapped, underfunded and under-resourced local authorities are but there's also a lot of crap, incompetent practice going on too that can easily be hidden behind the resource issues.
Can you check your local authority's procedures manual online? Many do have them and they're accessible to the public. If you can access them they usually have clear timescales for the adoption process and who should do what when. If they've not kept to timescales for no good reason then it's a simple case of maladministration.
Take a deep breath, this will be over one day and if nothing else you can tell your child/children how you pushed and hollered to get them adopted because they are important and you really wanted to become their legal parent.
Wishing you luck.