It says in my book...
...that you don't get the writing from the ideas but the other way round. You only need a fragment of a scene pictured in your head. Then start to write, and the rest of the ideas will come.
Well, it sounds a bit arse-about-face but it's worked for me today.
Finally this afternoon I got a decent chunk of writing time (by dint of ignoring several other far more important things that I should have been doing... but let's face it, those dust bunnies aren't going anywhere fast...) and forced myself to write a section I'd been putting off for ages because I couldn't think beyond the scaffolding (another thing it says somewhere is to beware of spending time writing scaffolding), and the more I wrote, the easier it got and the more ideas I had.
Maybe I should leave the dust bunnies to reproduce unmolested tomorrow too...