The Chancellor, George Osborne, has said the government will be watching petrol and diesel distributors “very carefully” to ensure they pass on oil price reductions to customers.
Oil has fallen from about $115 (£72) per barrel in June to about $84 per barrel, a decline of about a quarter.
In comparison, petrol prices in the UK have fallen from a high of about 131.7p per litre in the summer to 124.22p – a decline of about 6%.
Diesel dropped from 136.37p to 128.58p.
Campaigners argue that taxes account for the bulk of UK pump prices, and that the government therefore has more power to reduce prices than petrol companies.