The grounds, and their relative popularity, are different north and south of the border. In England, according to a report published last week by Co-operative Legal Services, the most frequently used ground is unreasonable behaviour (cited in nearly half of all cases). Adultery is becoming less popular - at least in legal terms - with only 15% of divorces now based on this compared with 28% in the 1970s. However, these figures are in marked contrast to the latest statistics for Scotland (from 2011-12) which show that of the nearly 10,000 divorce/dissolutions granted that year, 93% were based on non-cohabitation.
It seems that Scots are less keen on the so-called "fault" grounds, but this doesn't necessarily mean that we are more amicable when it comes to the divorce courts! Instead, these figures probably reflect the fact that while you can divorce on the basis of non-cohabitation in both countries, English couples must have lived apart for at least two years (with the other's consent), or five years (without it) while the corresponding periods in Scotland are one or two years. While England has desertion, which doesn't exist in Scotland, this also requires at least two years apart. So there's no evidence that adultery and unreasonable behaviour are any less popular north of Hadrian's Wall - it's just that English couples who want to divorce within two years are stuck with them!
In practice, although whether or not one has grounds is a factual question, it also has tactical and practical dimensions. Divorcing on a fault ground means setting out the gory details in the court papers (and in the case of adultery, serving them on the "paramour"). This is unpleasant, and since it's more complicated than non-cohabitation, also tends to run up more solicitors' fees. Most people prefer to avoid this and in the majority of the Scottish cases we deal with, the parties negotiate financial and child welfare matters and then divorce by consent after a year has passed.
Sometimes, too, the absence of grounds can also cause problems. For example, if a marriage has simply ground to a halt, with neither party behaving badly and no affairs, there are no grounds and so no divorce action can be started for at least a year. This can be frustrating if no progress is being made in negotiating a settlement, as the spouse who is keener to resolve matters cannot force the pace by going to court. Obviously the timescales are shorter in Scotland so if you are in this situation and think you may have a choice of jurisdictions, it's worth taking advice from one of our dual-qualified specialists.
A more drastic option might be to move somewhere like Illinois, for example, which offers no fewer than 11 grounds including "the attempt to end the spouse's life by poison or other means showing malice". I think that would probably count as unreasonable behaviour anywhere in the world, but in the meantime, if you're willing to wait, separation is still the lowest-conflict option both north and south of the border.