I'd say that becoming an ethnic minority in your own country is a massive problem.
If you're happy to be a minority in your homeland in 30 years time, then keep voting Labour, Tory or Liberal.
If you want immigration stopped, then you know who to vote for.
If you think about it, if it takes 30 years before the ‘whites’ become an ‘ethnic minority’, and if that means that they will suffer discrimination, than the ‘ethnic majority’ has 30 years to devalue a discriminatory view of minorities by treating everyone equally despite their numerical status. So if or when the time comes when the ‘whites’ are a minority, it will come in tandem with ‘British as the Majority’. At which time, the majority vs. minority distinction would have disappeared. To simply assume that the ‘majority’ always discriminates can easily be deemed to be a projection of one’s own attitude toward difference. And in the expression of this attitude lies one of the significant reasons why an excluded minority will have to be protected against as they might learn their lessons well from being excluded and become marginalisers if or when they become the majority.
(the above view does not apply to those cultures that deem difference an evil. But, given a multicultural environment, and time to be taught the value of difference, such a culture can be displaced or have discriminatory elements replaced with inclusive ones.)