Hiya,
Yes in 'General' it's a combination of things, as mentioned by bookgrl. The place all this happens - in effect - is on the stock trading floors and that's where any 'changes' are felt first causing a 'rippling effect' throughout the economy, the regional and then the world economies.
Food is a very prominent place where price increases due to the above and also local and national factors is felt by the general population. Ever since the recent 'big change' of the US Sub Prime mortgage fallout, Food prices was amongst the top items that were noted to get almost immediate price increases - along with energy prices, petrol pump prices. As alot of food is imported into the UK, the increased transport costs etc to get it here means it cost more further up the supply chain - net effect is the consumer pays more.
Be aware that other 'staple' factors will start to probably increase in cost/price - living costs, insurance costs, transport costs, borrowing costs (aside from interest rate increases) are likely to increase leaving less disposable income for most of the population.
Reign in spending everyone!
Cheers DtM! West London & Slough UK!