I've just reviewed this before posting so I apologise for it's long-windedness.
The single versus twin argument in this instant would depend on what performance was required - the whole point of "twin engine safety" is that you operate to a certain weight limit in order to acheive a certain performance. Simply put, if you want to fly away from an engine failure you load the aircraft to no more than a certain weight, and that determines the excess of single engine power. This means, hedsethair, that if the crew required safe fly-away performance, they wouldn't - or shouldn't - have the weight problems you suggest.
That opens up the rest of the argument, which is the difficult to quantify question of what is acceptable safety versus cost. Yes, twin engine operation is safer and of course it's more expensive. So is extra training, better equipped aircraft, employing pilots with much more experience, operating to higher weather/level limits. Apart from the last they all make small, cumulative, hard to quantify improvements to safety at extra cost.
As regards the UK record, there have been IIRC two major tail rotor problems, one due to human error during a daily inspection and one due to human error in a maintenance procedure. There have been the same - low - rate of engine shutdowns due to chips, overspeeds etc as in any other branch of the industry. Only a couple have gone Suddentwang and stopped, which again is about the norm. Pretty much all of these engine problems have gone unremarked because the aircraft has flown away on, err, the other engine. A preponderance of single engine aircraft would have resulted in most of these being precautionary landings, with the consequent risks especially at night. You pays your money and takes your choice... or rather the government does it for you, which IMHO is fine in this case.
The problem with the single/twin argument is that failure rates are quantifiable and can be legislated for- so they are, regardless of their frequency. The far more difficult problem is that human error causes most of the accidents, and that also costs, especially in training. There is a law of diminishing returns where more and more money results in smaller and smaller increases in safety; peronally I feel that the UK has gone as far as is necessary [for now] down the technical side but that the required training could be expanded.