An ongoing reform programme of the post-16 Advanced "A"-level qualifications in England and Wales means that pre-university mathematics content and assessment will change from 2017. Undergraduate engineering is a subject that relies heavily on mathematics, and applicants to engineering degree programmes in the UK are required to have studied A-level Mathematics in order to be accepted. Therefore, the planned reforms are likely to have an impact on students' transition to undergraduate engineering. To investigate this, we conducted an online questionnaire survey of 462 current undergraduate engineering students who had taken A-levels. Participants reported on their experiences of studying post-compulsory mathematics and the preparation it provided for their degrees. Those who had studied the more advanced A-level--Further Mathematics--in addition to A-level Mathematics, considered it to be good preparation. They also believed that the A-level structure, which allows specialization in certain areas of applied mathematics, to be advantageous. In particular, possibilities for in-depth study of mechanics and pure mathematics were highly valued by participants. It is recommended that university engineering departments do more to encourage prospective students to study Further Mathematics. However, it should not necessarily be made compulsory because of constraints regarding access, uptake and provision of Further Mathematics in certain schools.