No idea. I didn't really get the point you were making, as you said:
"However my understanding is that anyone landing in the UK not in a usual entry point or claiming asylum immediately is entering the country illegally. Most of those crossing the channel are in this category."
This doesn't really help as there was no mention of where "they" were landing and whether or not "they" had immediately claimed asylum. I was just putting a link up to some more info on the situation with regards to asylum seekers and you could then hopefully work out if it applied to "those" you were discussing.
I have no idea how many crossing the channel in such a way do either of these things, for all I know it could be 0%, or it could be 100%, or, more realistically, somewhere in between. The link just hopefully clarifies what the regulations are for those who are genuinely seeking asylum, whatever proportion that may be and hopefully we all don't assume that everyone who does it is doing it for the same reasons.