“Invasion definition, an act or instance of invading or entering as an enemy, especially by an army.”
Your definition of “invasion” is too narrow, Islay. As has been adequately demonstrated, an invasion is not restricted to those arriving as enemies (and even your own narrow definition does not provide solely for invasions by armies, only “especially” so). It is quite clear that the mass movement of people across borders for questionable reasons and without leave to enter is an invasion. However, it doesn’t really matter what you call it. It is unsustainable, undesirable, and unnecessary.
“Once we are out of the EU that will be a matter for them”
Alas our leaving the EU will not put a stop to the problems presented to the UK by this phenomenon, f-f. The masses will still invade mainland Europe, they will still move northwards and westwards, and many of them will still try to enter the UK from France. We are unlikely in the extreme to withdraw from the European Convention on Human Rights and repeal our own Human Rights Act meaning that those who do reach here illegally are almost certain to remain. The source of the problem for the EU is that the nations with external borders are unwilling to properly police those borders as far as their resources allow. They see their function as assisting the migrants into Europe and “resettling” them once they have arrived. Instead they should concentrate their efforts on keeping them out.
On a brighter note I was pleased to learn that one of the “fears” expounded by “Project Fear” - the removal of juxtapositioned border controls in France and the UK, facilitated by the “Le Touquet” agreement - has been firmly scotched by President Hollande. A number of regular contributors suggested that this was certain to be discontinued should we vote to leave; I suggested it was almost a certainty that the facility would remain.