Will gcse affect the chances of me getting into Loughborough product foundation year?

Specific GCSE requirements are not flexible - they are about the basic skills required for the course. If you apply without the right GCSE grade, you will be rejected. An additional A level in another random subject is not going to fix this. Loughborough is a top Uni for Engineering, hence their high standards - but there are other Foundation years at other Unis that will have lower GCSE requirements.

I see, the reason why I wanted to add another subject is because the non foundation year option (they accept level 3 + one required alevel) and they only thing the state about gcse grades is gcse English at 4/c which i have

I have just looked at these courses and I think you need to check the entry requirements with Loughborough. My reading is that you will require A level Maths in addition to a BTEC Extended Diploma for the main degree. Even with the 'smaller' BTECs, you are going to need Maths and an additional related A level - ie. "All offers include Maths and either Design and Technology or Physics." This is why they would accept the lower grade GCSE - because you would need to be taking Maths at A level.

Are you looking at the product design engineering or the product design and technology? I'm looking at the product design and technology which is;
BTEC Level 3 National Extended Diploma: DDM plus one of the required A level subjects at Grade B

Okay - but its still "A level at grade B in one of Physics, Maths, Further Maths, Electronics or Computer Science" - are any of these subjects, and achieving a grade B, going to be a realistic option with a grade 5 in Maths at GCSE?