IMO it will just split the Labour vote. Further-left parties don’t tend to do well in the U.K. anyway.
I’m afraid Farage will pick up a lot of votes, since he will ‘do a Trump’ in promising to tackle the issues that what they like to call ‘ordinary people’ are concerned about. So yes, the boats and immigration in general, among others.
In recent decades, the ‘right-thinking’ Labour elite have too often dismissed the concerns of ‘ordinary’ people, labelling them ignorant, thick, bigoted, etc.
And a bit off topic, I know, but IMO it’d be an excellent thing if all potential MPs were required to have worked for at least 5 years in a sector that is not local council/local government/ trade union official.
Whether that’d produce enough suitable applicants is the question, though.