That's bad news ... we had the same in Hampshire around this time of year for the last few years ... awfully sad as it is clearly people who know bees (I hesitate to call them beekeepers ! - More beetakers) that do this. It's not casual crime, it's planned and deliberate and pretty despicable in my book.
But ... with the value of bees - regardless of the hives and frames - the thieves have made an easy £1000+ for a night's thieving if they can find someone to buy them. They will probably end up as Nucs after burning the hives - they'll get an 'overwintered nuc with the queen' and another 'this year's nuc' out of each colony so you are probably looking at even more than a grand - even allowing for the cost of a few plywood nucs.
B....rds !!