Families have been warned that the prices of basic foods will rise steeply again because of acute shortages in commodity markets. Experts told The Times yesterday that prices of rice, wheat and vegetable oil would rise further. They also forecast that high prices and shortages — which have caused riots in developing countries such as Bangladesh and Haiti — were here to stay, and that the days of cheap produce would not return. Food-price inflation has already pushed up a typical family’s weekly shopping bill by 15 per cent in a year. Gordon Brown responded to mounting concerns about the global rise in food prices by signalling that he might scale back Britain’s commitment to biofuels, which critics say has exacerbated the food crisis because land has been given over to grow crops for energy rather than food.