Truthseeker
How did you get on, has anything changed? I was reading through your post and noticed
>>I actually like my work and enjoy many aspects of it, and I take pride in delivering good quality work so have no issue giving extra time rather than shoddy work<<
I'm sure this is why it is all falling to you - they know you will do whatever it takes to get it done. Perhaps you need to become a little less conscientious. Having said that, I know it's a very tricky matter.
At the end of the day though you have to draw a line in the sand about how many hours you will work per day and you can only do what you can do during that time. Communicate that to management and set their expectations for whatever you think the result will be. It's just not acceptable that they can just say, work till it's done if that's not doable. I know about the culture of fear etc, however it sounds like they would really go down the tubes if they lost you - they need to back off, start taking you seriously and come up with some other answer to their problems other than making completely unreasonable demands on you.