Go on then, I'll bite. This is exclusively about asylum seekers, not the far greater number of legal migrants? And the aim is to allow in genuine refugees but prevent unsafe routes such as small boats? Here is what I would do.
Proper reception centres for asylum seekers. I'm not talking about cramming desperate people onto prison ships, or detaining them, but decent self-catering accommodation with a hub at the centre for English lessons, legal visits, housing advisors, medical provision, education and so on. Such reception centres not to be mandatory (some will prefer to stay with family for example) but available. And staffed, properly, with staff fully trained on the risk of re-trafficking and alert to the risks of young people going missing. Electronic tags for adults where this is considered necessary.
Decisions to be made within weeks, not years. Immigration officers to be well paid and well educated, with some trained in particular asylum producing countries so that they don't write fatuous nonsense in the decision letter.
Where decisions are positive, refugees can remain in the reception accommodation for up to 2-4 weeks while arrangements are made to transition into the community, with the assistance of social workers, employment teams, housing and benefits advisors, so that they can move seamlessly into the community and either start working or continue learning English and volunteering (or similar). Refugee children automatically to have an EHCP.
Where decisions are negative, the individual gets a tag. Automatic legal aid, good quality advisors who will be realistic with them about prospects of success, Tribunal hearing pretty quickly. If the appeal is successful, then as above with the positive decision. But everyone comes back to court for their decision - just as we bring people back to crown courts for sentencing, we don't just write them a letter saying please go to prison.
If the appeal is dismissed, they are then detained straight from court while further appeal rights are dealt with, if they are subsequently successful then they leave detention, and if not then they are returned to their home country. Enforcement to be conducted primarily by specialist social workers and police, until immigration officers can be trained to behave decently.
For those who do not win but cannot be returned (some countries refuse returnees) they get 6 months leave at a time while arrangements are made. For families who lose, specialist social workers who help them to make arrangements for a safe return which might include looking at relocation in their country of origin or employability schemes.
Those who enter by small boat to get 3 months leave to remain pending their asylum decision if they are willing to give evidence about people smugglers. Eyewatering sentences for people smugglers, and no Prisoner Transfer Agreement available for anyone convicted of modern slavery offences.
Shit-hot information sharing about people smuggling and modern slavery with EU countries.
Obviously all of this would cost money, but clearly the govt have some down the back of the sofa as they found it for the hot mess that is the Rwanda scheme. The deterrent effect for small boats would be that the entire claim soup-to-nuts would take no more than six months, and there would be no post-Tribunal option of just fading quietly into the dark economy.