Trade uncovered over a hundred finalists in European space station (5,3)

'station' is the definition.
(BBC radio station)

'trade uncovered over a hundred finalists in european space' is the wordplay.
'uncovered' says to take the centre.
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'a hundred' becomes 'ioo' (IOO resembles 100).
'finalists in' indicates one should take the final letters.
The central letters of 'trade' are 'rad'.
The last letters of 'european space' are 'ne'.
'rad'+'ioo'+'ne'='RADIO ONE'