ccording to the latest polls, that lead is now just two points. With a hung parliament a distinct possibility, attention will inevitably turn to the Liberal Democrats, the party that could sway the balance of power one way or the other.
Roger Williams has been a Liberal Democrat MP since 2001 and as the party spokesperson for food and rural affairs, has provided a regular check on the current Defra set-up.
He says: "I think Defra has improved a little bit, but there have been too many instances of it failing to stand up for the interests of British producers, for instance over pesticide legislation. Britain did too little too late; had we built up a coalition across other countries then common sense could have prevailed."
An issue on which the Lib Dems have long been vocal is the creation of a supermarkets ombudsman, as Williams is keen to point out. He explains: "The Liberal Democrats have led the call for an ombudsman. The way in which horticultural producers and top fruit producers have been treated by the supermarkets has been absolutely appalling.
"The key thing now though is: are we going to get an ombudsman with teeth? It is in the supermarkets' interest to have viable producers in this country because there is huge demand for British products, and if people can buy British they will. But it can only take place if there is fair trade throughout the food chain and the ombudsman or regulator is key to that."
He would like a proactive regulator that can initiate investigations to stop supermarkets from "putting impositions on producers". And, unlike others in the debate, Williams would like to see the regulator's powers extended to include "non-edible things like flowers".
He is equally scathing about the actions of the sheds where 90-day credit agreements have been imposed on some suppliers: "I see that as part of the ombudsman's role as well. It wouldn't be something you would see in most industries where there is a balance between purchaser and supplier."
He acknowledges, too, that ornamentals producers got a raw deal from the introduction of the Technology Strategy Board (TSB). He says: "Peoples' interest in gardening is growing and peoples' spend on plants for gardens are increasing and I think we have got to have the money following where the success is and where the demand is. So yes, we would look to see that in the reprioritising of expenditure, that ornamental horticulture does get its fair share."
But, while Williams recognises the need for better research funding, he says it is not the public sector's responsibility to support near market research.
Instead he supports the idea proposed by a British Protected Ornamentals Association member whereby supermarkets either pay a levy or administer a levy - raised through the tills on behalf of ornamentals producers - that would see a penny in every pound going to support near-market research.
Like the two main parties, Williams talks of efficiency savings within Defra. He says: "It's going to be a shift between expenditure on administration and bureaucracy to one that helps commercial growers. That's the way we will test the proposals we'd be putting forward."
Williams has been involved in the debate on the water bill currently going through Parliament.
Although the HTA's amendment on hose-pipe bans was dropped from the bill at its last reading in the Commons, persistent questioning by Williams and others has secured some concessions.
Environment Minister Lord Davies said he would work with water companies through the statutory planning process during the bill's second reading in the House of Lords. Williams said he had received assurances from Environment Minister Huw Irranca-Davies to the same effect.
He is also keen to see soft landscaping used more, both to mitigate floods, and as a tool in combating climate change. Despite a general aversion to national targets, he says he would not be against replicating the German model whereby a minimum proportion of each new development should be given over to soft landscaping.
He was critical of the original peat targets imposed by Defra but says he supports a separation of domestic and commercial use for peat in any new targets that are set.
Finally, he calls for more apprenticeships and more school visits to rural industries. He will write to Defra to berate it for its failure to get the food and land-based industries prioritised in the recent BIS document, new jobs for new businesses. "That was a sign of one part of Government not understanding what the other part was saying. We have got to build up the esteem in which land-based jobs are held.
"It's part of a long supply chain, so first of all we have got to get Government to understand that it's got to be part of the priority again. One thing that's clear to us as Liberal Democrats is that we are not going to be able to deliver those public goods unless we have a profitable and thriving horticultural sector and agricultural sector, so key to us is a profitable use of land."
1966-9: Selwyn College, Cambridge, reads natural sciences
1969: Becomes livestock farmer and joins Labour Party
1981-2001: Breaks away and becomes SDP (later Lib Dem) Powys County
1985: Chairman of Brecon and Radnor NFU
1990: Chairman of Brecon Beacons National Park
2001: Liberal Democrat MP for Brecon & Radnorshire
2002-2005: Junior spokesman, Wales and food and rural affairs
2005: Member of the committee for environment, food and rural affairs
2007: Lib Dem shadow secretary of state for food and rural affairs