BB: Sorry, but you'll need a JAA examiner there to keep your JAA licence. - The cheque will not do. Don't know which tests would be involved though. I believe that depends for how long the licence has lapsed (and on the goodwill of the officer you are talking to that day).
OC: You wouldn't be flying an EMB145 for a well known and little loved Dutch company!?!
There are no validations for JAA licences in the UK. Not every JAR country does it this way, but the UK CAA will accept your Danish JAA licence including all ratings. you can of course swap it for a British licence if you want to, but I kept my Irish one for nostalgic reasons.