Who would be at fault in this situation

I guess your signalling may be ambiguous for approaching traffic, although I can understand why you did it.

As to the fault, both in legal terms, and moral terms, I'd place on the overtaking traffic - it's up to them to make sure it's safe to do so.

As to your road positioning I can understand your position, in trying to manage how much room, and at what point people try and overtake you. With respect to the fault thing, I'd still say it's the responsibility of the overtaker to ensure they can do it safely. As to whether it's "correct" from either a moral or legal standpoint, I'd say you need to ensure a reasonable amount of road-space, and as a cyclist (more occasionally, these days! ;-)) as well as a driver, I'd say it's a balance of ensuring that you have sufficient road space, whilst not being that obstructive.

And I recognise that the more you try and hug the left side of the lane, the less space many drivers will give you. However, whether the middle of the lane is the best way, or not is bound to be divided ;-) (if you'll pardon the pun).

The problem is, and I recognise it - minimising your own space as a cyclist, and drivers often take liberties, and don't give sufficient clearance, and often overtake when perhaps they haven't really considered the road ahead and approaching traffic. Take "too much" and you risk annoying drivers, but quite possibly being more safe in the main.

You are more vulnerable on a cycle, and ultimately self-preservation is quite an imperative. Personally, I probably wouldn't generally cycle in the middle of a lane, although I can recognise there may be specific sites where it may have some merit. I'd more likely make sure I had some space to the left of me - but it is a difficult situation, and I personally recognise that in some circumstances, if you don't you effectively court being run off the road.

It's a balancing act (sorry don't mean to go overboard on the puns ;-)), and one where you'll have to find your own levels of what suits and is safest and least risk - but at least you're thinking about it. The thing to bear in mind about your road positioning, and blame, is that a gust of wind could push you wide at any point, or it could be a horse or some other more slower moving road user that could be providing much the same obstruction hazard to vehicles wishing to overtake - so the onus is still on them to overtake where it's safe to do so.