I've just managed to resolve the issue on the Pokemon app and hopefully others but I've not got time to check.
If anyone is having this issue and can't find anything, please follow what I've found tonight (info was found on this site, however it was in German which I don't speak but after translating I've roughly followed it and it's worked).
1) Go to https://mail.google.com 2) Click the Settings icon above your inbox and then on the drop down box, press Settings again. 3) Along the top of the next page, click Accounts and Import 4) Change your email from *@googlemail.com to *@gmail.com.
This instantly resolved the issue for me, I really hope this helps other people that are having this issue! Original Poster Daniel Eccles marked this as an answer