Mariah sorry to hear about that
my uncle carried a large amount of money and had it taken off him by customs at the airport so he refused to fly and he had to get a solictor and get documation to show he had A, drew it out of the bank B sold a house were the lump sum had come from he then got it back and they told him to use bank transfers in the future!
Also years ago i had a unfortunate visit to my house by the boys in blue ( i know not customs ) and they siezed my car phones money jewelry etc to get it back i had to go to court and prove A it was mine B i had paid tax and how much i earned C all my documentation to procur said items etc
I eventually got my car, phone and SOME other items back . i had to show i was earning said figures .........i also got the vice in area where i worked to write me a letter to show the judge saying they knew of me
This wasnt anything to do with brothel charges etc
I dont know if you have a accountant or do your own books but i think a copy of your earnings , copy of adverts , copy of your ni insurance payments etc should do the trick take as much info as you can to the solicitors , as you will have to prove how you earnt it and break it down .
But i dont think ?100o cash is a lot of money in this day and age to carry on a aircraft .......it is scandalous especially as it will cost you time and money trying to get it back /prove it is yours ;-(