OK, slightly dodgy, but if you/OH can do it, then register as self employed, you're still allowed to be employed too.
You have to fill in a self assessment at the end of the year, but you can claim for legitimate expenditure such as heat/electric when you are working from home. You don't need a limited company/business, anyone can be self employed, e.g. I could do someone's ironing and charge say £5, it counts as self employed income, but also as hours worked.
HMRC ask for total hours worked, so long as that is over 24 hours, and who is to say what you work during self employment, you would qualify, slightly more work and you have to advise HMRC of the self employed income, if any, every six months or so, but at least you'd get more of what you should be entitled to.
Glad to see my accounts brain hasn't disappeared yet, lets see how it gets as pickle is closer to arriving!