Farming by its very nature is a human "artificial" activity; only when people are involved do crops grow in rows in fields and only because of human activity do our crop plants exist at all; none of them occurs in the wild in the form we use them.
GM technology is benign in the agricultural context. With a need to feed more than 6 billion people now and many more in the future, we have to grow crops in a more-or-less intensive fashion whatever we do. That clearly has had, and continues to have, an enormous impact on the "natural" environment and the wildlife that lives there. We as a society need to reconcile the two: growing the crops we need, while allowing as much wildlife as possible to flourish, and leaving adequate areas of land for recreation or as wilderness areas.
By reducing chemical usage and increasing yields, agricultural biotechnology makes fewer demands on the land and causes less harm to wildlife. Experience over several years in those countries which have been growing large quantities of GM crops have shown the problems to be minor and capable of being dealt with by sensible management practices.
All sorts of living creatures influence others in one way or another but the real effects on non-GM crops are likely to be trivial. Non-GM crops are, of course, the products of domestication and what is now considered as “conventional” crop improvement which is based, of course, on genetic change caused deliberately, thought imprecisely, by cross breeding or the use of mutagens. They are in many cases as "natural" or "unnatural" as GM varieties. But the biosphere is a global interactive whole and we need to manage biotechnology just as we do for all other agricultural activities.
The use of GM crops in agriculture is likely to have minimal effects on wildlife in the UK as it has elsewhere. The physical consequences of a little cross-pollination will usually be detectable only with sensitive laboratory testing. Most of the GM modifications have benefit for the modified crop only in the context of deliberate cultivation; GM plants have difficulty surviving in the wild because they are not competitive plants.
J.E. Carpenter (2001). Case Studies in Benefits and Risks of Agricultural Biotechnology: Roundup Ready Soybeans and Bt Field Corn. National Center for Food and Agricultural Policy, Washington D.C. (http://www.ncfap.org./pup/biotech/benefitsandrisks.pdf)
M. J. Crawley, M. J., Brown, S. L., Hails, R. S., Kohn, D. D. and M. Rees (2001). Transgenic crops in natural habitats. Nature, 409, 682-682. (also reported in The Economist at http://www.economist.com/science/displayStory.cfm?Story_ID=498471)
P.J. Dale, B. Clarke and E.M.G. Fontes (2002). Potential for the environmental impact of transgenic crops. Nature Biotechnology, 20, 567-574.
R.H. Phipps and J.R. Park (2002). Environmental benefits of genetically modified crops: Global and European perspectives on their ability to reduce pesticide use. Journal of Animal and Feed Sciences, 11, 1-18.
T. Gilland (2000). Precaution, GM crops and farmland birds, in Morris, U. (ed.) Rethinking Risk and the Precautionary Principle. Butterworth Heinemann.