There are four ways the UK can go from here with regard to Brexit, and all of them are bad. Read the first direction: hard Brexit, or no deal.
Second: soft Brexit, the EU’s deal
Hard Brexit will be unthinkable catastrophe for the UK, and cause some damage to each of the EU-27 countries. EU-27 are prepared and ready to offer a deal to the UK, but as EU-27 are better-prepared to negotiate, have better negotiators, and are in a stronger position (they can survive the damage done by no-deal Brexit; it is uncertain whether the UK can or not) the deal for the UK on leaving the EU will be set in terms that will favour the EU.
On 14th April 2011, David Cameron made a promise:
So, taking all this into account, I believe controlling immigration and bringing it down is of vital importance to the future of our country.
That’s why during the election campaign, Conservatives made a clear commitment to the British people…
…that we would aim to reduce net migration to the levels we saw in the 1980s and 1990s.
Now we are in government, we are on track to meet that aim.
Nick Clegg thinks that the problem with that promise was that it was undeliverable:
“I said to David Cameron he shouldn’t make the commitment because it was inevitable he was going to break it because you can’t control the net figure… We said we were not going to do it as a coalition government. It is very embarrassing for the Conservatives. They made a huge amount of fanfare about it and they were warned by me and others ‘Don’t do this, it doesn’t make any sense’.”
(If you are a white UK-born LibDem supporter, however, the Conservative/LibDem government responsible for this is “The best UK Government of my lifetime”, so there.)
Labour think they’ll pick up votes by pledging to have more controls on immigration.
(Though in fairness, Diane Abbott condemned the mug as “shameful” and the pledge as a problem, for which she was predictably condemned in the not-at-all racist Spectator. (There’s just something about Diane Abbott they don’t like.))