Whichever way you look at it, it's a shambles.
It was born out of the will to get out of Airwave as fast as possible because the original PFI terms were crippling.
The solution was not ESN, it was hold Airwave to account for the missed performance targets that happened every month, and withhold payment until they sorted themselves out. As Macquarie ran the business with an empty bank account, they would have been forced into administration, and HMG could have bought them for £1 - thus owning the network, and then only having the running costs to pay, not the exorbitant fees that they were being charged. They could then instruct Motorola to upgrade the network to TEDS2 or better, and then go out to tender for a composite device that could do high speed data over LTE leaving critical voice on the now government owned Airwave network.
Nope, can't do that because government seems to be allergic to owning things.
What we must also remember bus that EE won the network deal because everyone else pulled out, and Motorola won the implementation deal because... everyone else pulled out. They could see it was a poison chalice, and would be fraught with issues due to unrealistic timescales with it needing 3GPP standards that still don't all exist yet, and hardware that also didn't exist.
And six months ago they gave Crapita an expensive lifeline to do something that was already easily possible - a bit of VoIP routing. FFS you can do that with a Raspberry Pi and a copy of Asterisk!
Still, it's all keeping me gainfully employed!
I refer the reader to my subtitle.. omnishambles!