OBK!
DoMePlease makes some interesting points about the Far East where I am sure it is the norm to not wear a jacket and possibly not even a tie due to the climate. It goes without saying that that is not the norm here in the UK.
Valid points have already been made. Yes, shiny shoes don't make a good pilot, but they do make a good impression, which let's face it, is what you are after. £400 for a suit is more than you actually need to spend, but do go out and try lots on with someone (preferably female) with a sense of taste who can critically eye you up and down in each to say if they are 'you' or not. Above all, keep it dark (grey or blue seem best), not black! If you must get one with pin stripes make sure they are very thin and very faint, you are not trying to be a City Trader! Do make sure it fits you nicely; if you are an odd size consider getting it tailored (mainly leg length) as you can look rediculous in an ill fitting suit no matter how much you've spent. I would say belt rather than braces and DARK socks that compliment your suit and shoes, no pictures on them.......non of this 1980's sports socks(I can't believe I used to do that!!!!) Buy your tie at the same time so you can get the female to match a tie/suit/shirt combination; keep it simple and you won't go far wrong. Daffy Duck really must be held back for your first day!
It's personal choice but I would say single breasted rather than double, sensibly sized lapels and no more than 4 buttons (depending how tall you are) on the front (it's a business suit you're after, not high fashion), which incedently you will be able to wear again and again whereas fashion suits suddenly look silly 2 years later. In fact I retract, as once you are successful at interview and land that airline job your waistline will never be the same again...............! Never do all the buttons up as it looks like a coat, undo them before sitting down if you keep it on and don't wear a 3 peice or you will look like a bank manager plus offices are always heated/ cooled to be suitable for shirt sleeve order, so once you are in the interview ask if they would mind if you removed your jacket. They won't, even if the interviewer keeps his/ hers on, and you look a lot better than if you sit there melting in your jacket! You will be hot anyway due to self imposed pressure so select your shirt carefully. White or pale blue look very good, but be careful of making the Tony Blair gaffe of a nice blue shirt with really dark bits all over it as the sweat seeps through!!! White has to be the better. On that note, 100% cotton shirts feel great but look crap after 20 mins of wearing, whereas a poly/cotton mix irons very easily and doesn't crease anywhere near as much (all my issued pilot shirts are poly cotton). Don't drive to the interview wearing your jacket, hang it up in the back to keep that 'just dry cleaned' look. Oh, and above all else.........don't leave the 'Aquascutum' label sewn on the bottom of the sleeve!!!!!!!!!
Hair cut 'above the collar' not too much gel etc if you use it, good clean shave with a fresh blade to avoid 'pizza piazza' and clean finger nails/ hands unless you are an engineer type who can explain it away!!!
Hope that was of some help, Granny and eggs come to mind, but if you haven't interviewed before those are my recommendations based on 3 successful airline interviews and no failures yet..........
Good luck
PP
ps. As soon as you arrive at the venue, find the wash rooms and straighten your tie in a mirror, if your top button is clearly in view it will become a magnet for those talking to you.