So two days after stir up Sunday I've realised what went wrong - I didn't put the lid on the big pots I was steaming the puds in. I used Nigel Slater's recipe and when he said put lids on I just thought he meant the pudding bowl lids. 
Can they be saved? The suet hasn't melted, that's how I knew something was wrong. Can I steam them again now, properly, and then steam again on Christmas Day? Or are they well enough cooked that they'll keep for Christmas Day and I just steam it then (but for how long)?
Or bin and start again? Any advice welcome please. First attempt at puds, I thought I'd done so well.