It's a situation that could easily escalate into a major crisis. There are 3,000 migrants at Calais now - that could easily turn into 30,000 or 300,000 if word gets back to their countries that it is possible to illegally enter the UK and stay there.
Personally, I think that there needs to be a firm rule that anyone attempting to illegally enter the UK will lose any right to make an asylum application and will automatically be returned from whence they came.
At the end of the day, these people are heading for the UK purely because they see it as an easy life for themselves. A migrant from, for example, the Sudan crosses many other countries before reaching the UK - why did they not claim asylum in any of those other countries?