The last GCSE equivalent qualifications were awarded in 2014.
GCSE equivalent qualifications were accepted by some universities as an alternative to full GCSEs, but they may not have been recognised by employers and professional bodies.
GCSE equivalence meant that you had achieved a standard which was accepted as equivalent to GCSE by local higher education institutions, in the subject studied (English, mathematics or science).
Once you have been awarded an Access to HE Diploma, you have the qualification for life: the qualification itself doesn't expire after a certain date.
However, you should check with the university before applying because some universities have entry criteria that require you to demonstrate evidence of recent study. This means that the Diploma may have a limited 'shelf life' in this respect.
In addition, some subjects evolve and develop (particularly in technical subjects), and the content of Access to HE qualifications achieved many years ago may become dated. Such Diplomas may therefore not be considered to provide evidence of a suitable preparation for university-level study.