Maybe you need to look at this in the longer term.
If your husband is unemployed for over 12 months, he may become unemployable and never get a job. Assuming that you are mid 30s, you stand to lose out on a total of £360,000 before retirement. (This assumes he stays on £12k and never gets a pay rise).
See the job an investment - you lose at the beginning but so you can win in the longer term.
The other aspect you need to take into account is pension: how do you plan to finance your old age? If your husband is not working, it is going to be very difficult.
The costs of childcare will decrease when your child hits 2 years and the ratios of carers to children are allowed to get bigger.
Also look into Childcare Vouchers - this could save you £2400 a year in nursery fees.
In 18 months you will also get help with the childcare fees from the government with 15 hours free.
So why not let him try it out for a year, with the understanding that this time next year he will look for a better paid position.
He sounds like a decent guy - he genuinely wants to be useful when he could sit around doing nothing, so isn't he worth making a short-term sacrifice for?