Uk father and Spanish mother baby due 17/10/2018

[PatSmith]

Hi guys, I'm hoping that someone can help me please? My girldfriend is Spanish and is worrying about access for our son to the UK if she has our child in Spain. Basically she wants zero problems. Never mind Brexit, that's a whole other issue but, under the current laws which won't be changing any time soon, what will happen to our sons nationality? Will he be Spanish or will he be both British and Spanish?
Alternatively, does anyone know any official websites that I can go to and ask?
Thank you for taking the time :)

I think you need to seek specialist advice on this and not rely on Mumsnet! I am NOT an expert but a quick google suggests the child would currently be eligible for British citizenship but this would need to be applied for and not automatically granted, with plenty of supporting documentation required. I'd want to get it done pretty quickly too - before March 2019 and Brexit!
It appears much simpler if the child is born in the UK and has at least one British parent.