If you are y12 or y13 (or y14) you can do Maths & English at college if needed alongside another course.
If you are 19+ you count as adult education and can do Maths & English at college if needed though generally this will be evenings.
If you are 18 and post y13 and not at college it appears you can't do either.
However as soon as you turn 19 you are OK, but face to face courses will have already started.
So the solution seems to be wait for my autumn born to turn 19, then she can enroll in an online course and work through it at her own pace. For the online course, assessment seems to be online too - how does that work with exam concessions and prevention of cheating? Or have I got the wrong end of the stick?
I'm sure it should be more straightforward than this.