TIFU by not telling my employer I was interviewing for another job

I am a teaching assistant in the UK. Recently I have applied for a number of positions, and took time off work for one without telling my employer that I was interviewing for another job. Now another interview has come up on Monday. I haven’t told my employer yet, but prospective employer has asked current employer for a reference.

My motivation for not telling current employer was that they don’t have to give me time off work for interviews, and I was concerned that they would refuse. Background to this: I recently took holiday and departed a couple of days before my obligation to the school for holiday club cover ended (resulting in an ‘informal warnings that was, nevertheless, written.

I suspect I may just have to come clean and tell them I need time off Monday morning for the interview, but the optics aren’t great and they could refuse, which would obviously be quite the quandary and would look bad to both current and prospective employer.

There was no ill intent on my part, I simply wanted to avoid ‘going public’ with current employer until I had a ‘subject to references’ offer in hand, but it seems that’s not always how schools work, and references can be taken up prior to interview, as in this case.

Any and all constructive advice gratefully received, please! I’m stressed, upset and really don’t know what to do for the best…

TL;DR: concealed interview, now potentially caught between two stools.