When I worked for a bank in Australia the guideline was 10,000 AUD. Anything over this and we had to report it but I think that was more to do with money laundering, drug trafficking, funding terrorism etc. The most my foreign exchange here will let me send home onto my mortgage in Australia each month is 5000 GBP. I think for the same reasons. On HMRC it says they investigate anything over 15,000 euros.