Emergency credit
If you can not afford to top up your prepayment meter or you are unable to get out to top it up, your energy company will give you emergency credit. Emergency credit is usually around £10, which you should get automatically. If you do not get this when you need it, you can ask your energy company.
If you are vulnerable your energy company may agree to extend this emergency help on request. However, this needs to be paid back, and you will need to agree with your energy provider how you will do this.
More information
Citizens Advice and Ofgem have some useful information on prepayment meters and how to deal with your energy company if you have difficulties.
Fuel vouchers
If you can not afford to top up your prepayment meter you may be eligible for a Fuel Voucher to help you over the crisis.