Hiya LordFish,
There are a few "issues" with the online application form....
You should go to the first interview smart but casual, there is no need to wear your best... just dont turn up in your best tracksuit!!!!!
Your formal Selection Interview depends on a few things, the timing of your selection test, if you are successful at the test, the timing of your Presentation and if the job that your applying for is available or unavailable (if there are training slots available or not).....
Oh, also, Luton is a small office with a very limited number of staff... there are only so many processing hours in the working day, so dont get too upset if it seems that they are not processing you as quickly as you wish....
Hope this helps.