Wow...that sucks man.

I agree that it probably wasn't the best idea to go into detail about bitcoin to those CBP maroons.  I wouldn't talk to those guys about anything they didn't specifically ask about....especially anything more complicated than a ham sandwich.

Next time...ship all your electronics as a parcel before you leave.

Since you are British, perhaps you can fly into Vancouver Canada and cross at a land based border crossing?

IDK man...  better luck next time.