Thank you everyone for your advice and guidance.
OK- update. I have spoken to the chair and the preschool is not limited by guarantee, and they do not have trustee insurance.
He was seemingly confident that we didn't need it, as they kept enough in the coffers for redundancy. However, I expressed that I wasn't happy with this. He said that we could discuss it at the next meeting (mid-Jan).
I am getting a bad gut feeling about this- no trustee insurance, no electronic policies (and no mention of policies at last meeting), no new trustee induction, and I have had already had a disagreement with the nursery manager about her hampering parental involvement.
Should I:
a) go along to the next meeting with a summary of why we need the insurance, and bring along a quote. I have spoken to a couple of insurers on the phone today, and unfortunately it seems we need group cover at trustees- I can't just insure myself. And also press for electronic copies of policies that are circulated to all trustees.
b) Write a letter to the chair expressing my concerns, and agree to continue as a trustee only if the above are addressed and agreed at the next meeting.
or
c) Tender my resignation with immediate effect and bail now, and accept that this was a naive move on my part, and notch it up to experience.
I am the only parent trustee- the rest are church members/old parents. I feel that I could do so much, but feel that it is the blind leading the blind at this point. 
WWYD?
(oh, and clover kiss I haven't been asked for a CRB check! Luckily for them I have a valid DBS- Scouts and school volunteer- but they don't know this!)