using volunteer manager for UCAS referee when in full time employment?

[PoesyCherish]

Hi, does anybody know if this is okay? I'm currently in full time employment although am having huge issues with this (long story short I'm off on the sick due to a joint condition as work aren't making any reasonable adjustments to the working environment).

I've been thinking for a while that I'd like to go back to university. I've been volunteering with a charity for the last year. Does anyone know if it'd be okay to use my volunteer manager for my reference rather than my employer?

Does anyone know too if they'd want any info from my current employer? I really don't think my current employer would be willing to write me a reference and / or they'd use it as an excuse to get rid of me if they found out I was trying to leave to back to university iyswim.