Farmers are warning of a looming harvest catastrophe as wet weather threatens to wipe out crops, bringing concern over the future cost of some groceries.

The National Farmers' Union Scotland said harvest in many areas is already running two weeks later than usual because of the particularly cold and wet summer.

The situation is so bad it could threaten the future of some crop growers with NFU Scotland saying that because of poor market prices and higher costs a good spell of weather is needed.

Ian Sands, NFU Scotland’s crops chairman, said the impact on Scottish farmers could be critical.

He said "the adverse weather we have seen in recent months, coupled with the poor returns and high input costs, really threaten the viability of the cereal sector in Scotland".

He added: "With such a wet summer and now moving into autumn, many will also be facing additional drying costs in a year when prices are very disappointing."

Problems have been reported by farmers across Scotland and "all areas are suffering in some shape or form".

In Perthshire many have yet to start spring barley harvest, with yields of winter barley and oilseed rape so far below average.

For farmers in Ayrshire and Forth and Clyde, the situation is the same, with low yields and harvest running well behind schedule.

In Lothian and Borders, a slow harvest and colder temperatures has seen crops struggle.

In the North East, farmers have been seeing average yields, with wet weather, and many fields swamped while for some farmers in the Highlands, it has been the latest start they have had for spring barley harvesting.

NFU Scotland said it is a "bleak picture" for Caithness and Orkney, with harvest described as being some way off and low yields expected.

John Wildman, Ayrshire NFU Scotland regional chairman, called on people to back Scottish produce in the shops to help the industry.

He said: "Whether growing crops, keeping stock or milking cows, all parts of agriculture in this part of the country are struggling with low prices and the effect of the poor weather.

"Consumer support is key.

"We need to make them aware of the difficulty our industry is in and remind them of the fantastic products that our hard work underpins."

Mr Sands, whose farm is at Scone, Perthshire, added: "What really worries me is what will happen with malt barley if it gets rejected?"

He added: "Fertiliser manufacturers need to start pricing their products at a level that more fully reflects the fall in crude oil and gas prices.

“Fingers crossed but we desperately need a dry couple of weeks now to allow us to get the Scottish harvest back on track.”

Some dairy farmers threatened to cause disruption on the roads last month as the they stepped up protests over what they say is too low a price to produce milk.

It was reported there were warnings of French-style blockades as farmers claimed they are being forced to sell milk at well below the cost of production and are losing about £200 a in production.