LCD TV use output from ZX as interlaced screens. TV output from ZX is at 50Hz, but LCD TV connect each two screens to one visible TV picture. ZX output 50Hz => LCD TV output 25Hz. On LCD TV you can see 2x higher vertical resolution (even tv line = one zx tv frame, odd tv line = next tv frame).
Next graphic example:
https://velesoft.speccy.cz/other/scrmix2.zip
UNREAL SPECCY support this mode...