The Conservatives say immigration and asylum are running out of control and are using a full-page newspaper advertisement to trumpet their plans for quotas. Here's how the scheme would work and what critics make of the idea.
The newspaper advert was signed by the Conservative leader
What are these quotas?
There would be annual limits in three areas: asylum seekers, people wanting work permits and those coming to Britain to be with their families.
How would they work?
Parliament would cap each of these categories every year. In each case, the Conservatives say MPs would take into account factors such as shortages in the labour market or how wars may affect the numbers of expected refugees. Once the quotas were filled, other immigrants would be turned away. There would be 24-hour security at ports to combat illegal entry.
How would they decide which workers to let in?
There would be an Australian-style system where points are awarded for work experience, qualifications and languages. Work permits are currently given if a UK company can show an immigrant worker satisfies the criteria for one of a variety of schemes covering areas such as highly-skilled migrants.
How does immigration relate to the economy?
Many employers use immigration to plug labour shortages. A good example is agriculture: thousands come from Eastern Europe every year to pick British crops because farmers say they can't get local workers. Critics say that this is not the whole story and that employers should do more to look for staff at home before bringing in people.
For instance, should labour shortages in the Indian restaurant trade - a major problem at present - be solved by recruiting waiters from Bangladesh or more locally?
What about asylum?
The Tories want to process all asylum applications overseas so that only genuine refugees are allowed into the UK in the first place. Ultimately, they would like the United Nations' refugees agency (UNHCR) to allocate people to fill the quota.
Anybody trying to claim asylum in the UK would be taken to centres near their countries of origin to have their claims processed.
So there is an international dimension to this?
Absolutely - and this is where the Conservative proposals would probably face three challenges: one from the European Union, one from our own Human Rights Act (based on Europe-wide principles) and one from the UN.
What has this to do with the European Union?
A lot. For a start, official figures show that the largest single group of people migrating to the UK in 2003 were the 14,200 who came from within the EU. The UK remains at the forefront of the two key EU immigration policies: rules on asylum seekers and separate arrangements for the flexible labour market. The government thinks we benefit from both.
It believes joint arrangements on asylum strengthens borders and international measures against people smuggling within the EU.
It also claims the UK has economically benefited from allowing in workers from the new Eastern European member states.
Now, as part of these complicated arrangements, the UK has a string of agreements with its neighbours on how to deal with immigration. There is a strong suggestion from Brussels that the UK could not opt out of these arrangements at all.
So what would that mean?
Trevor Phillips, chairman of the Commission for Racial Equality, has asked the Conservatives to clarify exactly what all of this means. If they are going to restrict immigration, he argues, they would have to start with those moving within the European Union. If the party does not mean EU migrants, he suggests, then the policy would leave open the way for racists to put the "worst construction" on the party's message.
And what about the other international dimensions?
The UNHCR has declared it would not co-operate with the policy because the Conservatives also propose ditching the United Nations Convention on Refugees, the cornerstone international document that helps manage and protect those fleeing persecution.
But there are other challenges. It is almost certain some elements of the plans would face court challenges. For instance, if Parliament sets a quota of 1000 refugees and the 1001st is turned away, this may break both EU rules on definitions of a refugee and human rights laws.
Then there is the proposal to limit the arrival of families. British law is very clear that government has no business interfering in someone's right to have a family, unless there is very good reason.
So if 100 families are allowed to be reunited and then the 101st UK-resident migrant is told his wife and children can't join him, then we would almost certainly see a battle in the High Court.
How controversial are the plans?
Immigration and asylum often prove highly contentious issues but the Tories are confident they are tackling real public concerns.
They point to the problems which hit the government last year when the immigration minister resigned amid criticism of the way work permits were granted.
The Liberal Democrats say the plans are a sign of political desperation.
Labour, which is unveiling its own proposals in the next few weeks, says Tory plans to cut the Home Office budget mean they cannot police the scheme.