There's a good analysis by the BGA, LAA and BHPA online. Google "An analysis of mid-air collisions involving UK registered civil aircraft".
In the 37 years since 1975, disregarding hang gliders, 178 aircraft were involved in 89 mid-airs of which 38 involved 74 fatalities. So two fatalities per year.
Perhaps that explains why the various EC systems are getting the take-up that they have had.
If a system costs £2-3K installed, on the sums described a post or two ago, it's on the rational edge of behaviour to install it (though an individual pilot may value their life at more than the state does for investment purposes)
Flarm has high take-up because, at least at first, the entry cost wasn't too prohibitive, at perhaps £600, and the threat between gliders was relatively high (102 of the 178 involved mid-air aircraft were gliders or tugs).
ADSB to date has low take up because the costs have been prohibitive (this may change with LPAT).
PilotAware is demonstrating that at £200, it's probably almost an impulse purchase, and well below the threshold that make sense, so lots of people are buying it.
In all cases, of course, there is an issue of critical mass - there's no point in being the only pilot with an electronic conspicuity system in the sky. It's like being the owner of the only telephone in the world. Also, there's probably extra money that people will pay for situational awareness - for example, in the case of Flarm people are prepared to pay more to get information about people that aren't actually a threat to them.
Paul