For a foreign country, France has some quite agreeable
geography, and plenty of it. In fact, almost all the land
within France's borders is geography of one sort of another.
The problem, of course, is that France is already inhabited
(to use the term broadly) by the French. Meanwhile,
England
is pretty much hemmed in by Wales and Scotland,
and is fast running out of space.
The solution, of course, is to lacquer France.
First, we need to get the French people to vacate France
for a short while. This would need some delicate
negotiation, and perhaps some financial incentive, but I'm
sure it could be done. After all, it's not as if they have
much to do. We could even invite them all over here for a
bit.
Next, we start to lacquer France. I suspect a polyurethane
lacquer would work best, although one might also consider
something acrylic. Ronseal does a wide range, and I'm sure
one of their products would do.
We'd need to apply, oh, maybe a few thousand coats, so a
quick-drying lacquer might be a good choice.
Once the lacquer has dried, we just need to wait a while.
Many areas of land (including France) seep out methane
slowly. Under the layer of lacquer, this methane will
gradually accumulate, being unable to escape.
Methane is less dense than air so, eventually, the entire
lacquer coat will start to lift away from the ground - first
in boggy, methanogenic areas, but then nationwide.
At this point, we need a team of men with ropes and
weights. The weights are used to adjust the France-
shaped lacquer shell toward neutral buoyancy, keeping it a
few hundred feet in the air. The ropes are used to pull it
westwards and very slightly north, until it butts up against
Cornwall.
We then drill a bunch of holes in all the high points of the
shell, allowing the trapped methane to escape. The entire
structure will then settle down gently onto the sea, where
it will remain floating. Finally, of course we run a mooring
rope around the Isle of Wight to stop it drifting away.
The French can then return home, and we are left with a
France-sized floating island, full of geography (or at least
topography), empty and conveniently located.
As a bonus, the new land would already be populated with
the casts of French buildings; all that would be needed
would be to cut access doors and install floors. We would
also get a set of Pyrenees and Alps which, although not
habitable, could be used for storage.