Post on My3cents also. Keep your receipts.. but you are only entitled to payment for your actual reasonable expenses.
BMI are now part of Lufthansa, so they do have deep pockets, but don't expect them to be too generous. Glasgow in shorts and a t-shirt... that was brave, even in summer, but at this time of the year it's bonkers. I also have to tell you £90 for a pair of trousers is ludicrous.. were they Armani? You could have got some at Marks and Spencer, which has a massive store in central Glasgow, for £20. You could have bought a suit, two shirts and some underwear for £90!! I think you can make a reasonable case for replacement clothes but I suspect anything over £200 would be deemed excessive.
If they are not helpful, you can file a smalls claims court claim entirely online. The link is here:
www.moneyclaim.gov.uk
You will not be required to appear and the cost is minimal, a lot less than you paid for those trousers! I am not 100% sure if foreign nationals can use this, you will have to check, but I can't see any reason why not. If BMI fail to respond they will enter a default judgement. You could then have the fun of having the bailiff's go and seize an aeroplane until the settlement is paid. What fun!!