More detail needed.
What is your present Freeview setup?
Aerial to freeview box to main tv in main house then to ? etc. etc.
or is the one in conservatory completely separate freeview box with own aerial?
Also it depends on where you live for strength of digital signal.
Lots of factors to consider.
I've no knowledge of being able or not of using main wiring but doesn't sound right to me.