MPs are set to debate a motion urging the government to stem fuel price rises amid a public outcry over costs. Tory MP Robert Halfon's motion was tabled in response to an e-petition signed by more than 100,000 people and is supported by more than 100 MPs. The government plans to increase fuel duty by 3p a litre in January - meaning an extra £1.50 to fill an average car. It says prices would be even higher had ministers not scrapped automatic fuel-tax increases imposed by Labour. Petrol prices have tripled in the past two decades. 'Immense difficulties' Chancellor George Osborne scrapped the annual fuel tax escalator - a mechanism under which duty rose by 1p above inflation every year - and cut fuel duty by 1p in March's Budget. However, he has only postponed the planned inflation-linked part of the duty rise from April 2011 to January 2012, and from April 2012 to August 2012. Mr Halfon said high fuel prices were causing "immense difficulties" for small and medium-sized businesses, and that some low-paid workers were paying a tenth of their income just to fill up the car. In his motion, he urges ministers to consider whether current fuel tax rates are economically competitive; what impact they are having on economic growth and unemployment levels; and to examine the case for a price stabilisation mechanism to even out fluctuations in pump prices. The Treasury has already said it will introduce a "fair fuel stabiliser" to ensure price rises are capped to inflation when oil prices are high, with oil firms filling the gap by paying extra tax.