Agree with what whatever5 said. If it's a chronic health condition, then it should count under the Equality Act, and he should declare it to his employer in order to get any reasonable adjustments required.
However since he's clearly able to work, even if he can't perform as well, he will not be eligible for ESA (which is income for people who can't work).
There's a faint possibility he might be eligible for DLA/PIP (help towards additional costs of being disabled), because there's a component specifically for mobility. But if the episodes aren't frequent and he can still walk more than 20 metres without severe discomfort or harm, he'll just be expected to use public transport if he can't drive.
In fact, I would be thinking carefully about your family strategy and finances at this point.
It depends on your DH's job and employer, but he may be at risk of the awful trap that hits the mild to moderately disabled/ill: too well for benefits, not well enough to please employers. Your DH should be proactive about managing this situation with his employer, making sure they understand he is protected by the Equality Act and also finding ways to minimise the impact on his work. You do NOT want to be in the situation where he is pushed out for capacity/attendance reasons and then unable to find another job because of same.