The MoD introduced a PETF (Practice Emergency Training Frequency) in the early 90's (1993 I think), which was just after the 'Options for Change' and 'Front Line First' rounds of spending cuts, when money certainly wasn't around in abundance (compulsory redundancies in several tranches were run).
As far as I'm aware, the receivers etc don't need to be upgraded or need more pipework, but an extra radio box at the other end is required and the ability to transfer the new DF onto their 'big picture' of the UK would need to be installed - hardly bank breaking I'd like to think. The difficult bit would be getting a common freq UK wide.