I'm sure you're right outside London - I wasn't being clear. Basikerly, the relaxation of the trans-race rules came about because there is a racial imbalance between the adults esp. foster carers and the children.
As you say the time line is very odd for a drama set in the present - social work hasn't run like that for years - all the laws the plot relies on were binned years ago, and replaced with a not-so-new adoption structure.
Kiri has been waiting since she was 4 to have her fate decided, or at least signposted, by the authorities. Five years - v. the not-so-new 6 months' law? Which has just been refreshed so it's tightened up?
Another opposite-of-accurate plotline - the suspicious birth brother is seen as an aggressor. But in a third (and a reported third, ie a lot higher IRL) it's the existing children of a family who are attacked and hurt by the adopted child. One of the reasons adoptions 'disrupt' ie fail.
Out of date tosh, not sure why no one noticed.