Well, Im no expert, but 20k sounds a whole lot more reasonable than 8k.

But then, if you got a variation approved at a rate of £300 p/m for another 44 months that only brings in a further £13200 anyway.
I would in the short term try for a variation, as the experts have suggested. As you do have valid reasons. Just remember it is your variation request so make sure it is done taking all your new I/E into account, including all the costs of the baby.
If your variation is approved, then a bit further down the line surely 10k or so as a final settlement would be welcomed? But then, as I say, Im no expert - just another debtor...