This is why I think a composite system containing both fan convectors and
a
low output underfloor system would work most effectively in a kitchen. It
is, however, I concede, not the cheapest option by a large marign.

Christian, your logic is wrong. Once the heat output on the room rises
above its heat loss, it doesn't matter how its heated.

Not quite. Take an example:

The heat loss is 1kW and the UFH is kicking out a 1kW, which is quite
reasonable. A nice stable temperature.

Now start cooking at about 1.5kW. You are now shoving in 2.5kW which will
rapidly heat the room by 1.5kW excess. Even if the stat kicks in
immediately, the UFH will give 1kW for some time.

If you had a fan convector, it would shut down immediately, giving 1.5kW,
which gives only 500W too much, which could be easily dissipated by opening
an internal door and using the heat in other rooms.

If you had a composite system, you'd probably set the floor temperature to
25C, which is comfortable to the feet, but would not add significantly to
the heating of a room already to temperature, perhaps a few hundred watts at
most.

Christian.