"the premise that cost makes for efficient use of resources"
That's a completely FALSE premise to begin with.
Selling to the highest bidder doesn't mean that the highest bidder is the one which would make the best use of the spectrum. Much more likely is that the highest bidder is the company that will charge the end user £80 for a service that a lower bidder might have sold for £60.
Then there's the likellihood that bidders will put in bids for unnecessary spectrum, simply to stop competitors from getting hold of the spectrum they need to set up a competitive service.
Spectrum shouldn't be auctioned, it should be allocated for a specific service and made available to whichever company can guarantee to provide that service for the least cost to the end user.