V_G - they are wearing what AP1358 calls 'operational clothing', which is the nearest we have today to the War Service Dress that the RAF officers would have been wearing at the time of the escape.
Also, bearing in mind that the escapers included 2 FAA officers and Major Johnnie Dodge (who ended up in Sachsenhausen for his pains), the tri-service nature of the chosen dress seems somehow apposite for this occasion.
I thought it quite impressive that (thanks to the editing of the piece) Stu Atha managed to be simultaneously speaking at the microphone and sitting next to Air Cdre Clarke at one point in the news clip...