@Walter Hinteler,
OK, so from the UK's perspective, they give to the EU 1.2 Million people, but get back 3 Million. But there is also the issue of a great many former British colonies have people emigrating to Britain too, and that should be taken into account. I think the UK has a moral reason to have a high quota of allowing these people to emigrate to their once "mother" country. This is an issue most other EU nations don't have.
Don't forget, we are not talking about the UK rejoining the EU, we are talking about hammering out a treaty where trade between the UK and the EU would be enhanced in return for the UK agreeing to follow some EU rules. I don't see why any treaty has to allow entirely open immigration from the EU to allow lowering tariffs, after all, the UK is not a part of the EU, just a country that it is in the interests of the EU to make a treaty with.