The TV in question and thus I suspect the original poster is a British Model..
I often comment that we here in the good old USA do not speak English.
We speak American English. They are different.
And you have discovered, in this thread, one of the differences.
Ariel = Antenna in (Coax in on most TV's)
To the O/P I don't know about your side of the pond (Atlantic Ocean) but often those connectors are crimped on and not very well. if the connector has slipped a bit or if the center wire is cut too short connection may NOT have been made.
Unscrew and remove the cable from the ariel connection the as you push it back on feel for the center wire to make contact. there will be an increase in resistance If you do not feel the added resistance re-dress the cable (remove connector and replace) making sure you cut the center lead about 1/8" longer