Legally I am not sure what the correct answer is.
However, I do not people who have been asked to change how they do things or given more responsibility working hours etc. effectively changing their job. they then approaced their employer saying that their old job is effectively now redundant and they are not able to do their current job so is their any chance of a redundancy offer being made.
that being said I know these people hated their job and were going to leave anyway but were just chancing their arm asking for a settlement package. Also, this happend almost 12 months ago when there was a bit more cash floating around.
I note that you say you are 6k underpaid however, the grass is always greener on the other side and in general in the past 6 months most if not all industries appear to have cut wage by about 10% along with a policy of not hiring any more staff.
So I think you need to ask yourself can you definately get work elsewhere. That being said hating going to work everymorning is a terrible state to be in and can really affect you and your family so that needs to be weighed up to.