Let's look at the facts
The obvious solution, and one that was discussed 5 years ago when I was at the HO, was to use the public 4G network with -
1) Emergency Services had handsets that signalled to the base stations to give priority/exclusive use - this is part of the 4G spec.
2) Public money was used to build masts in areas that weren't commercially viable but were needed to give coverage for emergency services
3) Public money was used to build masts in very high demand areas such as football stadiums.
The last 2 meant tax-payers would benefit from the £M spent.
I recall this option was rejected due to 'securidee' concerns in favour of splurging £B on a dedicated 4G network.