doing masters while working?
I am currently doing the exact same thing you are wanting to do: working full time as a data engineer and pursuing a Master's degree part-time in data analytics. It took me a very long time to find a program that was focused on BI or anything near that since it is still a relatively new field (new as in gaining traction in academia). Also, Business Intelligence is very wide, it encompasses a lot of different things. University College London (UCL) offers a part-time master's degree in Data Science which encompasses some BI stuff and more. If that's not exactly what you meant by "BI", then I would recommend searching for schools in London (or worldwide, in which case you'd be looking for online programs - which is also very possible) that offer a BI program, and then seeing if it can be part-time or not.