Fitted the third incarnation of Evgeny's remote tailgate module. It now works. There seems to be a need to keep the button pressed until the tailgate starts to move down but this can be seen as a safety feature minimising the possibility of a guillotine effect of the descending tailgate on unsuspecting passersby!
I like this mod , especially for use from the dashboard tailgate button. It came as standard on some of my daughter's cars in the USA and I was always jealous.