I can only speak from my perspective as a UK subject.
Islam is in a mess. Many of the Muslim countries have civil wars or strife. People leaving their home countries just shows what a vast problem there is.
I once was an immigrant. In the 1950's my family with me emigrated to Australia. The locals were as welcoming as some of your answer-ers. I was bullied, our car headlights were smashed; graphited etc. We were called parasites, we were blamed for every crime going etc... and we were invited to emigrated to Australia.
How much more to be forced from your home; to flee from war and persecution; to be fleeced of your money; to risk death (thousands have died)... all this and to arrive in a country that pores more hate on you from the start. So strange - so strange.
So why do they come:
Well it certainly is not the 'benefits'. Those who are after them will go to Sweden, Germany or Denmark.
It certainly is not the weather.
Is it for the work? Is it because the UK has a reputation for justice and fairness? Is is because we speak the language of the internet?
I do not know... Has anyone asked them?
So what effects and problems?
1/ Their culture is so very different... so very alien. This leads to misunderstandings which can lead to clashes.
2/ as part of that culture is their religion. This is a distinct problem as it has very different morals. This is already causes massive problems as theirs is very primitive beliefs. The concept of blaming women for man's sexuality has been challenged in the UK. In Islam it is still considered the woman's fault if she is raped. (Mind you some Neanderthals of the UK who think the same)
http://www.bbc.co.uk/news/world-middle-east-36516006
There is also the problem of Sharia Law. Great Britain is (somewhat) a democracy. Having parallel or separate laws cannot be tolerated.
Also the problem of terrorism. Most, by a vast number, are not terrorists. However, where there is turmoil, opinions and behaviour polarize. This trows up extremism. We have already seen this.
Now, the idea of a refugee compared to an immigrant is that refugees usually go home when the war / political situation clears up. However, when reading about the the Middle East, I see no resolution.
What can we do? I wish I knew!