Gave this a test this evening. The SG is down to 1.016, which seems a little high so might leave it another day or so. As ever, I tasted the sample and it had a good level of sweetness and was very bitter (probably something to do with the slapdash way I measured the hops), but this should mellow after some conditioning.
My main worry is that it looks very cloudy and there were large chunks of what appear to be spraymalt floating about in it. I guess this is down to me not mixing the extract in well enough before the boil but I don't think it will effect the beer particularly. I really hope it clears well in the keg, or it'll be a bit disconcerting to drink.