If you haven't seen it yet, the Museums Association's MUSEUMS IN THE UK 2017 REPORT is an interesting and useful read.
The results of a UK wide survey, the survey’s respondents equate to roughly 22% of the UK's museums. It sheds light on many anecdotal and conversational "facts", reporting the real numbers and experiences to say that there are national highs and lows, and where there are differences between different museum types or locations.
Clearly laid out, with explanations to help interpret the statistics, and some pull quotes from respondents, this is a well considered survey, well interpreted, and undoubtedly of use for further advocacy work.
Even if you just read the Key Tends page, grab a brew, have a look, and consider where your establishment fits into this picture.