My recollection is that decision was a straight-up "success is irrelevant, HM Treasury has decided that the UK cannot afford to have an orbital launch program".
From the timing, one certainly could speculate that the needed pounds were being squandered on other programs - ones given higher prior, but less-competent leadership.
Wikipedia's version: https://en.wikipedia.org/wiki/Black_Arrow#Cancellation
From the timing, one certainly could speculate that the needed pounds were being squandered on other programs - ones given higher prior, but less-competent leadership.