Pethidine is the narcotic drug that will most likely be available to the woman during her labour. Pethidine is stocked in all delivery suites and in some birth centres. The drug is a legally restricted medication that is locked up on the hospital ward. It must be checked, recorded and accounted for by two caregivers. In some hospitals it is also the policy for the 'checking' caregiver to stay with the 'administering' caregiver until the drug is given, therefore witnessing its administration. (This is to guard against the uncommon, but possible, abuse of the drug by any hospital staff).
As midwives cannot prescribe Pethidine for women planning a homebirth, it may be obtained by asking your local doctor (or GP) to write a script and have this filled in the last weeks of the birth. Some women will organise Pethidine (or hire gas) 'just in case' they need it for their homebirth, but may or may not use it. Others (especially if they have used Pethidine in a previous labour) will know that this is what they want to use. If the Pethidine is not used for the labour, the medication should be returned to the chemist who issued it.
Discuss the option of Pethidine with your caregiver. Bear in mind that in reality, Pethidine tends to be used fairly infrequently in home and birth centre births (even if available). This is because the woman usually uses natural forms of pain relief and possibly gas. If these are not effective then there is a tendency for the woman to then just opt for an epidural, skipping the Pethidine.
Caregivers who work in birth centres and homebirth will usually be reluctant to use Pethidine in labour because of its unpredictable effect on the baby. It is generally undesirable to have the baby born at home with the possibility of their breathing being suppressed, due to being sedated by the Pethidine.