"Consider this - it is often those women with difficult labours who are offered and generally the epidural (i.e. basically they would have needed an instrumental delivery even if they had declined the epidural)"
I would love to see some research which compares outcomes for women who've had elective epidurals (ie - low risk women who have decided prior to labour to opt for an epidural), with low risk women who opt to try to labour without an epidural and who are offered one to one support in labour and the option of an active birth instead.
Personally I'd eat my hat if the rates of instrumental births weren't higher in the elective epidural group. It's just basic physiology: epidurals turn your pelvic floor to mush. This means your baby is less likely to rotate effectively into a position which will expedite birth, and also that it's harder for malpresentations like OP to be corrected in labour.
I've just been looking at an Australian population based study on interventions in labour. (data from 363000 births)
The figures for low risk primips were:
No epidural, no induction: 11.8% ventouse/forceps (1.7% c-section)
No epidural, induction, 17.9% ventouse/forceps (3.4% c-section)
Epidural, no induction, 36.7% ventouse/forceps (31% c-section)
Epidural, induction, 36.7% ventouse/forceps (33.51% c-section)
Striking I think.
Back to the issue of causation (below, from the same article)
"The one prospective randomised control trial which was 'uncontaminated' by high rates of crossover from the experimental to control groups and vice versa, found the relative risk amongst primiparous women of having a caesarean section following an epidural during labour was 11.4 times greater. That trial was stopped on the grounds that it was unethical to continue to randomise because of the statistically significantly increased rates of c-section amongst those with epidural pain relief"
RE: the OP, my personal feelings are that it's completely unethical for a midwife to deny a mum access to epidural anaesthesia in labour, once she has established that the mum is able to make an informed choice. I understand why midwives do it, but it's WRONG.