Based on the fact that the OP describes them as "scraping around the bottom of the middle classes somewhere" (great expression if difficult situation) I'm guessing that the OP is earning about £40k and her DH is earning something materially less - say £25-35k. The three factors we don't know are: (i) where in the UK they live, (ii) what their housing situation is and (iii) how many children they have and their ages.
I'm the same age category as the OP and, honestly, it's a nightmare age because it's really too late to change careers, and changing careers and getting to a meaningful level for any period is pointless. My DW is currently retraining to be a teacher but she has a few advantages: (i) our children are now all of school age and I can do drop offs and some pick ups, (ii) she wasn't educated in the UK so can get a state loan for the cost and (iii) we live in an expensive part of the UK so there aren't so many people chasing teaching jobs.
I also know many women whose husbands have lower (or minimal earnings). Some women are fine with that, but as children get older and costs increase I see more and more cases where the wife resents the husband for "not pulling his weight". The thing is, men in their 40s aren't going to change their careers/lifestyles. To some extent, women actually have an easier time trying to turbo-charge careers in their 40s because the perceptions that they may have put career on hold for a few years when they had children or that their career may have been impeded by sexism. The men I've seen who turbo-charged things in their 40s are those who are self-employed or set up their own businesses - it's virtually impossible in an employed situation.
This issue is actually less of a big deal when the wife is a very high earner, e.g. >£100,000 because then there is just more money to go around. Where the wife is the higher earner but not actually a particularly high earner IYSWIM as things are more stretched. The issue also tends to crystallise in late 30s/early 40s as up to then it's perfectly possible that spouses are on different career tracks with one earning less early in career but with a greater payout later or there's just the possibility that something may happen. Early 40s you start to realise "this is as good as it gets".
Without wanting to generalise, I see this phenomenon as very much more in some societal groups than in others. I don't think UK society tells women that spousal career/earning power matters and there's almost a sense that it's not something that should be commented upon at all. By contrast among my south Asian friends, career/earning power is referenced quite openly as a consideration - and not just in terms of prospective husbands but also prospective wife's. I'm not sure that just telling women not to be financially dependent on a man works for those other than the top 5-10% of earners because (again, depending on a bunch of other factors) only those can afford to raise a family without a second income.