TV signals are broadcast mostly hoizontal polarity, but many are elliptical favouring horizontal to mitigate multipath somewhat.With anomolous propagation there "could" be a polarity flip in some situations, but I think most of the time the polarity should be the same as the station broadcasts.
I would build as long of a yagi as possible (limited by rotor, tower capabilities, and site dimentions of course) centered in the VHF low band.
Best luck would likely be picking up stations in the Canadian maritime provinces and NE US states. Not sure if Gander NL has a TV station, that would be the closest to Europe. Look at "great circle maps" for beam headings. Just checked, there is a CBC transmitter at St John's NL on channel 8 or 183MHz if the data I am seeing is current. That's VHF high, less likely to see propagation, but you never know!