Electrical Site Bollard Trip Protection

I have read in the "Caravan Magazine" of a product that apparently qoute "allows you to set a limit on the amps coming into the caravan to just below the campsite average, thus preventing you from tripping the RCD at the post" unqoute.

Has anyone come across this? if so what is it called and were can it be obtained? Unfortunately the info in the mag is a little vague, but I presume that it would be hard wired after the intake socket, if it actually exists at all.

In anticipation thanks for the info