Help gaining copy of GCSE results

Hi I just wondered if anyone can help me?

After several house moves since taking my GCSEs I cannot locate my certificates and have concluded that I will need to apply for a replacement however I am unsure how to go about this due to the fact I have no ID in the name I was under when taking my exams

When I was born I was registered under my dad's surname but my parents were unmarried and split shortly afterwards, by the time school started my mum registered me at school under her name and had no problems with that, then once I was 18 she told me I had to make a decision as to which name I would be known as and as legally (on my birth certificate) I was already under my dads surname I decided to carry on under that name not really considering the fact my GCSEs were taken under my mums name

Now to apply for a copy of results they are asking for ID for the name as it was at time of exam and I have no ID under my mum's name I was wondering if anyone had been in a similar situation or if anyone knows how I can go about gaining a copy of my results?

Thank you