British fruit and vegetable growers have expressed outrage at a decision by Home Office ministers to close a 60-year-old seasonal migrant scheme under which east European workers have picked a third of the UK's fresh produce crop.

Amid fears of a rise in supermarket fruit and vegetable prices, the National Farmers' Union has warned that the decision will put thousands of existing UK jobs at risk and have a devastating impact on the horticulture sector in Britain.

Peter Luff, the Conservative MP for Mid Worcestershire, accused ministers of making a serious misjudgment about the state of the market: "Fields of vegetables and orchards of fruit will go unpicked in the next season. The experience of decades is that British workers don't want to do this work. They are temporary jobs," he said.

Meurig Raymond, the NFU's deputy president, said the fruit and vegetable industry would suffer without access to a reliable, flexible and consistent source of migrant seasonal workers.

"Our grower members will be rightly outraged at this decision. Make no mistake, this will cause a contraction in the British horticulture sector, one which is already suffering from falling self-sufficiency levels. It will put thousands of existing permanent UK jobs at risk, stifle growth, compromise food security, and jeopardise the industry's efforts to take on hundreds more UK unemployed for permanent work."

The decision has been made despite a warning from the home secretary's migration experts that a failure to extend the scheme will lead to a sharp rise in fruit and vegetable prices and job losses in Tory heartland seats.

The immigration minister, Mark Harper, told MPs on Thursday that the seasonal agricultural workers scheme, under which 21,250 Romanians and Bulgarians have come to Britain every year for a maximum of six months, will close in December. The scheme has provided a third of Britain's seasonal agricultural workforce.

Conservative MPs from Kent, East Anglia and Herefordshire have strongly backed a National Farmers' Union campaign for the scheme to be extended to migrant workers from Ukraine and Russia to maintain the supply of fruit and vegetables to British supermarkets.

Harper rejected the option to open the scheme to non-EU migrants, saying: "Our view is that, at a time of unemployment in the UK and European Union there should be sufficient workers from within those labour markets to meet the needs of the horticultural industry."

Harper said that while the scheme had provided an efficient supply of labour for the fruit and vegetable industry for many years the government was now looking at ways of helping unemployed British workers into fruit and vegetable work through training and guaranteed interviews. "A pilot scheme to encourage unemployed UK residents to apply for, train and secure jobs on arable farms has shown encouraging results with a high proportion of participants going on to secure employment in the sector. We aim to build on this," Harper said in a Commons written statement.

Harper said British growers currently recruited about half of their pickers from Poland and other eastern European countries who joined the EU in 2004, and about a third from Romania and Bulgaria. "Seasonal agricultural work can pay good wages and the sector should be able to attract and retain UK and European Economic Area workers," he said.

The official migration advisory committee said in May that British farmers should be able to recruit a sufficient number of seasonal fruit and vegetable pickers in the first year or two after the closure of the scheme.

But it warned that there would be a lack of available seasonal migrant labour, leading to a rise in labour costs and to a 10%-15% rise in supermarket prices. It expects Romanians and Bulgarians to be attracted to higher-paying jobs in urban areas once the labour restrictions on them are lifted this December, although some will continue to come fruit and vegetable picking.

Conservative MPs, including Peter Luff in mid-Worcestershire and Harriet Baldwin in Worcestershire, earlier this year pressed strongly for the scheme to continue and argued that it had a good record of workers returning home after completing their contracts.