Visa and asylum fraud is not widespread. My mother used to work in visa and asylum policy, and she is at pains to say how uncommon it is.
Yes, the small boat arrivals of people are very visible, but they are not very frequent. A lot of money is spent on accommodating asylum seekers, but most of that money goes to the accommodation providers and only a tiny portion to the asylum seekers themselves (£9.95 a week for those in full board accom or £49 a week for those not in full board accom).
Electoral fraud by ‘people with anti-Western views seeking to subvert our democracy’ is a constant threat, as shown by Russia’s increasing attempts to influence our elections, but it’s very well managed.
I’ve not yet seen any reports of terrorist or criminal fugitives entering the U.K. illegally. Most of them are removed successfully. I’ve not come across any evidence of lawyers successfully arguing for their right to stay in the U.K.
As for murders and raped committed by foreign nationals, these happen but they’re rare, and most of the time, the people committing them are here legally. I’ve never heard of a gang rape being committed in the U.K. by a foreign national. If you’re referring to gang rapes committed by grooming gangs, these are extremely rare, and the men committing them were British nationals.