Spot on Matt!
I decided to remove the length of fuel pipe running to the rear aswell as the still connected filter so I could work on the problem on the bench.
I sliced through the fuel pump threaded end using the dremmel so I could remove the union fitting that would normally unscrew.
It's exactly as you say, the union fitting has flared out noticeably . There's no way that it could be unscrewed without causing a load more damage.
I've decided to replace the rigid fuel pipe that runs to the rear, it was corroding a fair bit under the rear axle.
Not sure whether to make up a copper pipe or buy an original from Toyota.
What a pain in the arse,it should've been straight forward.