Well I mean, I don't know much about either uni but this it what I found out after a 2 minute google search:
Newcastle requirements:
"If only one of Biology and/or Chemistry is offered at A or AS level, the other should be offered at GCSE grade A or 7 (or Dual Award Science grade A or 7).
Once the academic criteria have been met, academic achievement is not considered further in subsequent parts of the application process e.g. additional A levels or A* results or additional GCSE results are not considered."
Leeds GCSE requirements:
"All applicants must offer the following GCSE Subjects or accepted equivalents.
We expect candidates to have obtained a substantial number of GCSE passes, at a high standard. At least 6 grade Bs must be offered including the following:
•
Dual Science/Double Science, or Chemistry and Biology"
What Leeds says about resits (this is about A levels but I assume their GCSE requirements are similar):
"We will also consider applications from individuals re-sitting exams where there are exceptional circumstances. Well-supported documentary evidence of any extenuating circumstances is required and you should use the UCAS form to explain this."
I assume that this means that you could apply to Newcastle but not to Leeds unfortunately. In order to make sure it would be best to contact the admissions people at both to ask about your circumstances.