here's a problem, firstly this is based on those that are either caught or do present themselves. there seems an assumption that all those crossing do so. secondly, during the week have heard a half dozen migrants speak and every one of them spoke of wanting to make a better life, education, provide for their family, they want to work. i say good for them, but it does rather run counter to the not economic migrants story.
im baffled why anyone would leave the safety of Greece, Italy, Spain, Germany, even France, and risk thier life again. obviously they think their opportunities here are better than those places, again contrary to many opinions of this country.
With regard to the first highlighted comment, I don't recognise the reasons for coming to the UK as a simple dichotomy in the way you do, i.e. migrants are coming over because they are being persecuted OR to get a better life for themselves and/or families; in my opinion the factors are not generally running 'counter' to each other so much as 'together'...
As has been mentioned by others here, there seem to be a variety of reasons for them to choose Britain, such as: being able to speak English (which may be very important in getting a job), family contacts in the country, perceived racial tolerance etc. Perhaps the matter is not as 'obvious' as it might at first appear.