ok quick update,
I got one of these,
pH Electrode with 300cm BNC Cable and Solutions
https://www.amazon.co.uk/gp/product/B00MGDWZ9I/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
Its a non-branded and only £25, works great, and at the moment holds it calibration really well, can recomment it.