It probably would be better to repeat the year. Maths has a major problem in education. I wouldn't know. I've never taken them before. I took it at the end of my Lower Sixth year, in modules - but further maths is a different matter altogether.
STEP is impossible in places.
If the single maths A'level were harder it would put many capable students off. Let the able and enthusiastic do further maths as well - it will stretch them, believe me. Maths is not so much getting easier as getting accessible. Hopefully the new AS system will help this. If so, then make contact .