Cloudbase is irrelevant when it comes to Cat I operations. Only RVR counts.
This then is what Southend should end up with when the lighting is finished. Info from Wikipedia
Category 1, Decision Height (above threshold) 200ft RVR limit 550 m or 2400 ft (1200 ft is approved at some airports)[3] Visibility 800 m.
I am getting confused with cloudbase and decision hight