There is no chain at either end of the transaction. It should be really simple. I'm essentially paying my solicitors a huge sum of money in return for a stressful, frustrating, ill-informed state of limbo. They're very good at the:
"We'll find out and call you back* in ten minutes?"
[* this is actually a lie]
...trick, for example.
I can only assume that my documents are lying near the bottom of someone's priority pile, wrapped in red tape.
So, another six weeks of phoning them every day to go then maybe - just maybe - I'll be living back in good old SE5 again. Fingers crossed.
September 29th - update
The lady selling the flat to me has apparently fired her solicitor for not being proactive enough. So, it's not just me feeling the frustration then.