I recall a storm-in-a-teacup about Fiona Bruce wearing a cross. The BBC said that she could wear a cross as long as it wasn't as big as the one a bishop wears.
Yes, you've got to be consistent. If you accept one, it's difficult to object to the other.
A hijab that is worn the way Fatima wears it and a small crucifix are not intrusive (I guess that Channel 4 and ITN reckon that most viewers are used to seeing women wearing hijabs). However, a turban would be intrusive (An issue that is unlikely to arise because there is no male mainstream British broadcast journalist who is a practising Sikh).