Blue-sky thinking has a role in policymaking. yet some ideas leaked from uk government brainstorming over where processing centres for asylum seekers might be located south atlantic islands, old ferries, even disused north sea oil platforms range from the foolhardy to the absurd. britain faces growing numbers of migrants, illegal and otherwise, coming across the channel. the issue exercises a portion of the electorate. a more effective system of control is clearly needed. but efficient should not mean inhumane.

Cross-channel migration poses practical and political problems for boris johnsons government. some 5,000 people had crossed in dinghies by august 31 this year, against 1,890 in all of 2019. kent, where most arrive, is running out of capacity to deal with them. rightwing politicians such as nigel farage, the brexit party leader, have made this a campaigning issue. the brexit supporters who constitute mr johnsons cabinet campaigned on taking back control of uk borders.

Paradoxically, brexit will complicate the issue and is one reason the government is exploring new solutions. the dublin regulation allows eu states to return asylum seekers to the first country in the bloc where they made a claim, or have been resident for at least five months; fingerprints are stored in a central database. the dublin system places an unfair burden on border states such as greece and italy, and has defied reform efforts. but once britain leaves the system when the brexit transition period ends in december, it will become harder to send migrants back to other eu states. those whose asylum claims are refused can potentially be returned to their country of origin, but the process is complex and often fails.

That makes asylum processing centres based offshore seem worth considering. home secretary priti patel is not the first uk minister to examine the idea; tony blairs labour government did so in the early 2000s. the likelihood of ending up in such centres with no chance to slip away and merge into society as when migrants are already inside their intended destination country seems a potential disincentive to attempt border crossings. governments legal responsibilities under international law are blurred.

Yet in australia, which for years operated migrant processing facilities in papua new guinea and nauru, such centres proved hugely politically divisive. human rights groups pointed to numerous abuses. holding vulnerable people in facilities that often lack proper services, legal advice and healthcare can lead to physical and mental health problems and even suicides. even then, the disincentive effect for desperate migrants is less than governments expect. considering such an option contradicts the home offices pledge to become fairer and more compassionate after the windrush scandal, and risks further tarnishing the uks reputation for respect for the law.

In reality, britains island status means it faces far smaller migrant numbers than similar-sized countries on the european mainland. the costs are not huge. processing centres on uk territory, where rights are properly protected, are an option. but britain also needs to step up co-operation with france, belgium and the netherlands in shutting down smugglers gangs, and to seek agreements with eu counterparts on return of illegal migrants.

The minimalist approach the government has chosen to future co-operation with the eu will hinder such efforts. how it chooses to tackle the migration issue, however, will say much about exactly what kind of country mr johnsons post-brexit global britain aspires to be.