Back in the days of my direct acquaintance with West Africa, before Nigerian oil, when life was little more civilised, Ghana and Nigeria enjoyed a sort of see-saw economic cycle. When one was doing well, the other was doing poorly, and vice-versa. Accra is separated from Lagos by a skinny strip of land that gives mini-nations Togo and Benin access to the Gulf of Guinea - generally migrants drive straight across it unhindered. And so with economic boom and bust a horde of migrants moved back and forth between the two cities.
And when some diplomatic spat or financial disagreement caused the two governments to fall out, the consequences were felt by the migrants. They were simply expelled en masse; rounded up by the police and army where necessary, and sent packing. I remember seeing two pieces of news footage; one was of Ghanaians trekking westwards, a long walking column of chaps carrying washing machines on their heads, women bowed under the weight of huge blanket-wrapped bundles on their backs as they walked home. The second was of Nigerians expelled from Ghana walking eastwards, a long column of men with fridges on their heads and women dragging cloth-wrapped bundles on makeshift sleds.
They're quite used to this sort of solution, you see. The hundreds of thousands now illegally in the UK would not be at all surprised and only slightly put-out to be marched onto a fleet of ferries moored at Southampton to take them home. It's the African way.