Right Andy, and anyone else it might help - but don't go by my word, I'm not an expert and my vision is pretty clouded by fury on this.
I've been reading and reading the guidance on the UKBA site, and the scenarios, and there are a few ways of meeting this - in fact this is about the only part they have been anything like "fair" - they could have said pure base income and nothing else, but they haven't.
So -
1. - The simplest one - earn £18,600 or more a year before deductions. Simple and it's on your P60.
2. - Earn £18,600 in one tax year, can include overtime, can include a hundred jobs, as long as they add up to a pre tax income of £18,600 in that year - again, it will be on your P60, or you might need to just produce wage slips to add up to this.
3. - Have a shedload of savings over £16,000 to make up the shortfall - anything over £16,000 can be counted as income apparently. Hmmm, weird.
4. - You don't even have to have a year of income, if for the last 6 months your income would lead to a yearly income of £18,600, this will do - so yes, you could work overtime or get a part time job for those 6 months. Seriously, yes it's barmy as overtime isn't guaranteed, but they count it - so lets be thankful there hehe
5. - Another way of having £18,600 a year - if for example you had a P60 showing £17,000, but then in one month you earned £1600 in overtime, well that would be enough - you have earned that amount - submit the relevant wage slips.
As I said, this is what the scenarios state, it's not my interpretation, it's all there.
On the other hand, you do have to have been earning that amount which will add up to £18,600 for the magic 6 months. Doesn't matter if you suddenly get a job paying a thousand pounds a week - you have to have been doing it for 6 months.
Hope this maybe helps someone.
Oh and I'm currently enquiring with my mp if benefits in kind can be counted as income. I'm not expecting a reply soon as she's notoriously slow to reply to things, but I even spoke to her a couple of days ago about it - we can see, but let's not get hopes up too much on that.