Fuel prices set to fall as oil price plummets after Russia lifts export ban
- Diesel and petrol prices set to drop after Russia lifts oil export ban
- Brent crude oil price falls 10% this week to $84.23 a barrel
- Biggest weekly fall in fuel costs for over a year
- Comes after oil traded above $96 a barrel just last week
- Fuel retailers previously boosted margins by delaying price cuts
