Even if it's conceded that the original 3G licence auction maximised the prices paid by the operators, and this didn't result in higher prices to the consumer on the grounds that they were sunk costs (more debatable) and that it didn't adversely impact other aspects, like network investment and thereby economic activity (even more debatable), then there is a much more fundamental reason why the exercise can't be repeated.
That's because at the time of the 3G auction, there were more potential bidders for bandwidth than there were available chunks of spectrum. In addition to the incumbents, there were a number of other operators seeking entry into the UK market including the (state backed) France Telecom and Deutches Telekom. It was this unique blend of ambitious operators and limited supply backed by inflated telecom valuations (and some de-facto state guarantees) that drove bid prices far past their economic value. Once the shareholders and financiers came round to noticing this, the supply of ready money dried up and auctions all across Europe then got fractions of what was achieved in the UK and Germany.
These circumstances will never happen again. It doesn't matter if there are 3 or 4 operators. The costs of entry into the UK and building a new network are immense. The only way that spectrum prices could be manipulated upwards would be to offer fewer chunks of spectrum than there are operators. By definition, that will lose one operator from the new spectrum. It's quite possible that one of the weaker players might decide the whole thing is not worth pursuing anyway and seek to either run as a low cost operator on existing spectrum or pursue other options. Of course if the spectrum is auctioned off such that all operators can get a chunk, then that's less of an issue, but it will not, of course, recreate the circumstances of the 3G auction.
So now that the fit of hubris of 2000 is over, there is no way that the telecom companies are ever going to fall for this again. The 2013 auction fell short of government targets by about £1bn (it raise £2.5bn vs the £22.5bn of the 3G auction). The circumstances at the turn of the millennium are not going to repeat themselves.
There's also another issue. Seeking to maximise the value of the spectrum to the state simply in the capital cost of the license, rather than through more continuous revenues from taxation on increased economic activity is surely short sighted.
In any event, 3 or 4 operators. It's not going to make a great difference to state revenues. The CEO of Telefónica César Alierta, has noted that the industry is not going to play ball with states that manipulate the circumstances of an auction in order to maximise a one-off return.
(nb. in the US, a similar auction approach to that which was eventually taken by the UK government in 2000 was ruled illegal and had to be retracted.)