Make up a very dangerous lead with the generator connected to one end
and a
3 pin plug on the other, then plug this into a socket on your ring main.
This will back feed the whole ring main, so ensure only the devices you
want
to run (taking into account the power of the generator) are switched on.

All very dangerous advice as well as highly illegal and you might well
find yourself in court on a manslaughter charge.

Surely the only way this can be illegal is because there is not a fool proof
method of disonnecting the house from the grid ?

Paul.