Beet growers could be heading for the third biggest crop on record as the campaign runs into the final stages, said farmers' leader William Martin.

The remarkably mild weather, which enabled beet crops to add weight, has boosted the potential national average yield to about 70 tonnes per hectare.

'My guess is that we'll end up with the third best ever,' said Mr Martin, chairman of the National Farmers' Union's sugar board.

'It is a pretty good result considering the conversations that growers were having in May last year,' he added. At that time, there was concern at the impact of the long cold spring, which hit emergence of many crops across the eastern.

The campaign is not set to end until the first week of March as Wissington, near Downham Market, which is the world's largest beet sugar factory, and Newark in Nottinghamshire, will be the last to slice out.

Although precise dates for the two other factories have not been confirmed, Bury St Edmunds, which has processed a much greater volume of beet than expected, and Cantley, near Acle, may end rather sooner, possibly in the last week of the month.

British Sugar estimates that about four per cent of the crop remained in the ground, with the highest levels in east Norfolk. Sugars were still holding steady at about 17.5pc in the Cantley factory area.

Mr Martin, who farms at Littleport, near Ely, still has about 400 to 500 tonnes of beet awaiting delivery. 'But they've been sitting there for about the past three months,' he added.

While he accepted that they had lost some sugar because it has been so mild, at least the wheat drilled behind his beet looked very good.

There was a feeling of optimism at the latest British Beet Research Organisation's growers' conference at Peterborough. 'Farmers were by and large feeling quite confident and optimistic about the crop which is a good thing,' he added.

The crop had continued to grow through the autumn and winter months. Fakenham-based Plant breeder Richard Powell, who is managing director of the UK arm of Strube, said that some growers had lifted crops at 65 tonnes per hectare adjusted in September while others had now harvested in excess of 75t, 85t or even 90 tonnes because the crop had just kept growing.

There was a hint of frustration voiced by some growers that British Sugar had been unable to keep all its factories processing at the maximum rates because of concerns about lack of storage. It has indicated that sugar production would be about 1.28m tonnes.

'I would rather have farmers ringing me to complain they can't get their huge crops into the factory than telling me that their crops are rotting in the fields because it was too cold. I know which one I'd like better,' he added.

Mr Martin understood the frustration. 'I know why it has happened because the crop is much bigger than British Sugar thought it would be when they made their plans. Growers would rather have the beet in the factory but the late delivery allowances has been a step up,' he added,

The continued crop growth had been 'unbelievable' and it is still growing now, he said. When a crop can add about 30pc in growth and sugars between September and early December, it has just kept going,

In the east, growers had been doubly fortunate because it had been milder and also drier than in most of the country. On his farm, he recorded a total about 85mm of rainfall last month but not the 200 to 300mm that many others have had.

'We are not as wet as we were 12 months ago. A year ago around there were lakes in every field, this year they aren't,' he added.

A record beet yield of 75.6 tonnes per ha was achieved in the 2011 campaign ahead of an average 71.7 tonnes in 2009.