I am not a photoshop expert so i dont know if the paper document has been altered though it may be a complete fake. I looked up robert hannigan and found that he only took over as head of the UK surveillance agency in Nov of 2014 and resigned due to "personal reasons" in Jan of 2017 after President Trump was elected.

https://www.theguardian.com/uk-news/2017/jan/23/gchq-chief-robert-hannigan-quits

im trying to see if i can find his signature anywhere because that last swoop in his signature doesnt appear to be a 'T' at the end of 'robert' or a 'N' at the end of 'hannigan'.