The aim of the project is to provide English Nature with evidence about the potential rate of formation and spread of 'stacked gene' volunteers of oilseed rape and the management of these plants in order to be better able to advise DETR (now DEFRA) in the risk assessment process. This has involved discussions with UK consultant agronomists and scientists before and after a visit to Manitoba and Saskatchewan in October 2001.Systems of farming in the Canadian prairies have become very dependent on glyphosate.  Despite this, the widespread presence of canola (oilseed rape) volunteers that are tolerant to glyphosate has not compromised these systems.It is concluded that herbicide tolerant gene-stacked volunteers of oilseed rape would be inevitable in practical agriculture in the UK. It is recommended that more emphasis would have to be placed upon post-harvest cultivations in order to minimise volunteer populations in subsequent crops. However, it is considered that there would be little impact on other agricultural practices if only genetically modified (GM) varieties tolerant to glyphosate (Roundup Ready) or glufosinate (Liberty Link) were introduced into the UK. The main implication for herbicide use would most likely be the increased usage of paraquat +/- diquat pre-drilling of crops. This might have an impact on hares.Discussions with consultant agronomists suggest that UK farmers may be more likely to try to control feral rape populations on uncropped land if they were to contain herbicide tolerance genes. It is recommended that more emphasis would have to be placed upon preventing their establishment in uncropped land and on methods of control that would have minimal or no impact on biodiversity.