This is quite a grey area. I've also considered selling knitting and other handcraft patterns, but this is what I've found out from other, more experienced people [but not lawyers by any means]:
First, only old patterns, from before like 1910 or so, can be safely sold under your name. Copyright issues here. Apparently as soon as you set pen to paper to write a pattern, your work is copyrighted. As in, no reproduction for profit by anyone else without your express permission. [But good luck enforcing that in court.]
Second, apparently you can take someone else's pattern, make enough alterations to substantially change the pattern's results by 10% and then call it your own pattern. I know I routinely do this for my own projects -- meaning I make changes to what the original pattern was.
Third, if you have created your very own pattern out of your oh-so-brilliant mind, then it is yours to do with as you will. Sell, give away, squirrel away in your cupboard away from any other prying eyes, whatever.
Eventually I want to sell at least some of my patterns on my website, but that's yet in the future. And I am likely going to offer up ones that generously follow the 10 % or more changes rule and ones that I've made up myself.
Hope this helps. It's a verry grey area. And regarding those "antique" knitting patterns - who's to say someone else hasn't beaten you to that old pattern and already made it their very own, so that if you try and do it - you're [innocently] tramping on their copyright.
I doubt that many of these issues actually get prosecuted. But it's not my style to tempt fate.
Hope this helps,
PS - I just noticed that you're in Scotland! The guidelines I've cited above apply in the USA - don't know about Scotland or the UK.