Campaigners against genetically modified crops are calling on the UK Environment Minister to stop trials in Wales - after he intervened over tests in England.

They have seen as encouraging the decision by Michael Meacher to question similar trials in the Midlands.

Mr Meacher has said that planting GM maize at Ryton in Warwickshire would threaten Europe's biggest research centre for organic crops - and he has asked the company involved to find an alternative site.  He told BBC Radio 4's Today programme he was concerned the crop could cross-pollinate with organic seeds.

GM trials have to be conducted at least 200m from the nearest conventional crops.

But the minister has said that the Ryton trial should be stopped - even though it is two miles away from the prestigious Henry Doubleday research centre.

"It has a worldwide reputation and if it were allowed to go ahead, the GM pollen could cross pollinate with three crops of organic sweetcorn that are grown at Ryton, and that in turn could contaminate the seedbank," he said.

"Any trace of GM in the research centre's fields could lead to the loss of licence from the Soil Association to grow organic crops.

"That would be a disaster."

The Welsh campaigners now want Mr Meacher to intervene to halt trials at three sites - two in Mathry in Pembrokeshire, west Wales, and one at Sealand in Flintshire, north Wales.

There were protests at the sites on Monday, as anger at plans to proceed with fodder maize trials continued to grow.

In Pembrokeshire, protestors converged on fields in Mathry which are due to be planted later this week.

And at Sealand in Flintshire, where GM maize has already been sown, campaigners were urging the landowner to destroy the crop.

More than 100 people - many driving tractors or riding bicycles - staged a slow drive around the two fields at the proposed site in Mathry, Pembrokeshire, west Wales, which have been ploughed ready for planting.

Some were dressed as the 19th century Rebecca Rioters -  complete with Welsh costume with blackened faces - to show their concern for what they described as a social injustice.

The land is owned by former Conservative MP Tony Marlow, who has listened to their worries, but remains determined to continue with the trials.

Protester Tom Latter said: "It was a very peaceful demonstration that showed the strength of feeling in the area."

The demonstrators are now proposing to take legal action in a bid to stop the crops being planted, and have been staging fundraising events to pay for a barrister.

Plaid Cymru MEP Eurig Wyn has said he may raise the issue of trials in the Petitions Committee of the European Parliament.

He said: "I share the concern of many other people at the non-democratic nature of this imposition on the people of Pembrokeshire of trials to which so many people are opposed.

"Many other matters of this nature have been the subject of appeals to the committee in the past and I shall certainly make every effort to represent the people of Pembrokeshire if it is their wish to proceed."

Meanwhile, at Sealand in Flintshire, a protest meeting was held at the land where farmer John Cottle planted GM maize seed on Saturday.

Between 30 and 40 placard-waving villagers staged a peaceful protest outside Birchenfield Farm.

They had the chance to put their points to farmer John Cottle, but they failed to persuade him to change his mind.

He was standing firm on his belief that the trials were necessary and would prove harmless.