IIRC this was passed at conference when the MP's had all scuttled off back to Parliament when it was recalled (when the poroguing of it was ruled illegal).
Labour maintain that immigration is not a problem, the issue is purely structural, build more houses, schools, GP's etc but with totally open borders how could you ever keep up? We could never hope to meet any environmental targets. I for one don't want to live in a place with no green belt or parks . We are already a very densely populated island and have not been non self sufficient in food production since before WW2. A ot of UK land is not suitable for food production or house building. Most immigrants want to live in the cities, not in the Highlands. As a country all our institutions and jobs are too London based . Water per person will also become an issue and we can wave goodbye to state pensions and benefits. Highly diverse societies are not know for generous state welfare. If Labour think that it will "buy" them votes in perpetuity then look how Blair's policy worked? They will have no hope of putting the services that unfettered immigration requires (housing, health, language help to name a few).
I don't think any of the main parties want to curb immigration. I suppose the Tories have put in some roadblocks and talk tough on it (as they know they need to win votes and some people will hold their noses and go for them). Labour if they persist with open borders will lose. Remember how successive politicians said that very few people would choose to come to the UK when the EU opened up FOM for the accession states. How did that work out?... brexit