There is the emissions issue... There's been a lot of claims bandied about that cars (on average) are more efficient at 60mph and that limits should actually be dropped. But frankly, sod that
If we're going to limit vehicles based on emissions, then it'd make more sense to limit inefficient cars to 60 and fit a tacho, and let efficient vehicles off the leash.
While cars have got better- chassis, brakes, tyres- and that decreases stopping distances and increases safe speeds, I'm not at all convinced that driving standards haven't fallen to compensate... But on the other hand, most of the drivers that are a real hazard aren't massively more dangerous at 80 than 70, and those that are, are probably doing 80 anyway.
Then again, an artificially low limit never gets taken seriously, and eventually just gets ignored.
Loads of alternatives mooted... faster "overtaking lane" with strict rules as posted earlier- but does that make things too complicated? You know people would sit in it regardless of enforcement. One slow lane and everything else faster? So trucks, caravans and 125 owners can sit happily in the 60 lane without having faster traffic crawl all over them.
Either way, I'll probably be exceeding it on long motorway legs anyway, so it's probably not that big a deal for me
But, if they were to increase the limit to 80 and enforce it strictly, that'd pretty much suck.