It's unlikely that we will see single engine IFR in the UK in the near future. I stand to be corrected, but I am only aware of one helicopter (the Bristow Jetranger) that is cleared for this, which I believe can only be operated IFR when conditions are such that in the event of an engine failure, wx conditions are such that a visual recovery is possible.
But even if we do allow single engine IFR, this will not prevent CFIT accidents. The problem is cost. Obtaining an IR is expensive, prohibitively so for most pilots, and to be confident you need to remain current. The equipment requirement is also going to prevent the use of most small piston helicopters. It isn't simply a case of a few hours instrument appreciation and a change to the rules, as it would be foolhardy in the extreme to start a trip VFR and then change to IFR as and when conditions demand. How many pilots flying VFR are aware of their MOCA/MORA should they wish to climb? And knowing that the cloud base is 1000' at your destination does not necessarily allow you to remain above MSA until visual.
You will not find me going IMC in a Robinsin R44, legal or not; and I have a current IR. Forget having only one engine, that's the least thing to worry about.
