Price of wheat up by as much as 5.9% while price of corn rises by up to 3.7% in response to the situation in Crimea

Wheat and corn prices have risen sharply in response to the crisis in Ukraine, which is one of the world's biggest exporters of both crops.

The price of wheat for delivery in May rose by as much as 5.9% to $6.38 (£3.81) a bushel on the Chicago Board of Trade – the biggest intraday rise for almost 18 months. Corn for delivery in May rose by up to 3.7% to a six-month high of $4.81.

Corn prices rose last week in Ukraine as farmers held back grain to protect themselves against the country's falling currency.

Ukraine has become an important crop exporter. It was the fourth biggest seller of corn last year and is set to be the sixth largest wheat supplier this year.

About 85% of wheat milled in the UK is home-grown and the rest comes mainly from the European Union and Canada. Much of Ukraine's supply goes to the Middle East and north Africa, and it is a bigger supplier of corn than of wheat.

Gordon Polson, director of the Federation of Bakers, said short-term market price rises would have little immediate impact on the cost of a loaf.

"The likes of our members buy a lot of wheat and flour but they have got very long-term supply chains. If there was to be a long-term spike, as a consequence of Ukraine or not, that would send up the price of bread. It depends on the wider harvest in the northern hemisphere. It might be a little bit more expensive but if the French and the Germans have a good harvest we should be OK."

Rising food prices, including for staples such as bread, have contributed to reduced living standards in Britain, especially for the poorest. But Jack Watts, an analyst at the Home-Grown Cereals Authority, said rising prices were caused by bad harvests over a prolonged period starting in 2007 and ending in 2012.

"If it's a sustained and large increase in price, which it isn't at this point, then Ukraine could have an impact but bear in mind that prices are still lower than at the end of 2012," Watts said.