A former Scottish Liberal Democrat MEP has been criticised for joining a lobbying firm that represents a genetically modified food giant months after losing his seat.

George Lyon is working on the agri-business account for public affairs company Hume Brophy, which counts controversial multinational Monsanto as a client.

Campaigners yesterday called for strict new rules curbing the "revolving door" that allows ex-politicians to reinvent themselves as lobbyists.

Lyon was a LibDem MSP between 1999 and 2007 before losing his Holyrood seat and becoming an MEP in 2009.

He sat on the powerful Agriculture and Rural Development and was a staunch support of GM technology.

In 2010, he criticised a European Commission proposal giving power to Member States to unilaterally ban commercial cultivation of GM crops.

He lost his Brussels seat in May and has now become a "senior consultant" for a lobbying firm with extensive GM interests in Brussels.

Hume Brophy, which said Lyon's appointment reflected "our ambition to expand our growing agri-food practice", has offices across the world.

Lyon noted in the same press release that Hume Brophy is "clearly a leader in devising and implementing public affairs and communication strategies specific to the agri-food sector".

According to a transparency report lodged with the Brussels legislature, Monsanto, the US-based firm that was the first to genetically-modify a plant cell, is among the lobbyist's top clients.

Hume Brophy has seventeen people accredited for access to the European Parliament and the former MEP will also be focusing on EU issues.

However, Lyon's appointment has again raised questions about whether restrictions should be placed on ex-politicians becoming lobbyists.

At Westminster, former civil servants and Ministers who take up a post within two years of leaving office must apply for advice on the suitability of a new job.

No such rules apply to former MEPs.

David Miller, a professor of sociology at Bath University, said:

"The news that George Lyon is joining the revolving-door gravy-train from the European Parliament to the world of corporate lobbying fits an increasingly worrying pattern."

"The European Parliament has virtually no rules restricting MEPs from taking up lucrative posts in business or lobbying after they leave office. It is high time that effective action was taken to close this loophole. There are plenty of precedents such as the US where elected representatives have a 'cooling off period' before entering the revolving door."

Lyon has also been accused of failing to declare his lobbyist link in a daily newspaper article earlier this month.

He joined Hume Brophy on January 1st and, two weeks later, wrote a piece defending GM technology:

"The EU has been left looking rather stupid as it tries to justify to our trading partners why GMs are blocked despite the fact their own independent food standards agency keeps giving them the all-clear."

"Meanwhile, around the world millions of hectares of GM crops are grown and millions of people consume them every day and despite the best efforts of the green NGOs to find problems none have been identified."

His consultancy was not mentioned.

Alan Smyth, an SNP MEP said:

"George is free to be as extreme on GM as he likes, and is free to voice his view, but he should be open about whose shilling he is taking.

"George has every right to be Monsanto's mouthpiece, but his views should carry a suitable hazard warning label so people can judge how impartial those views are."

A spokeswoman for Hume Brophy said:

"The most recent column George wrote in the 'Press and Journal' discussed the recent vote in the European Parliament regarding legislation on the cultivation of GM crops in the EU. During his time as an MEP, George was involved in the European Parliament's internal negotiations on these proposals.

"The views expressed in the column were entirely personal in nature. They reflect opinions long held by George on issues such as the challenges facing European agriculture and the role of science in risk based policy making."