I am very happy to do that. A number of noble Lords asked me to write to them on various technical aspects and I will do that. That letter will be sent out on 11 January, a week ahead of Committee stage.
My noble friend has raised one of the elements which is a problem. It is that we do not fully understand the scale of the problem. We deal with estimates. Even when the ONS undertakes forecasts, they are based on estimates. With effect from April, there will be exit checks and therefore we will know who is coming into the country and who is leaving the country and will be able to deduce by fact how many overstayers or illegal migrants there are.