Many thanks for your reply, yes my understanding was also that 2018 is the "new" start date for ESA IR managed (forced) migration to Universal Credit however I wasn't entirely sure of this. You're also quite right of course that these things are always subject to change!
I just used the benefits calculator suggested within this thread and it says the below....
"We have worked out that if you claimed Universal Credit your total benefits would be £23.68/weekly more than under the existing benefits system."
Damn, have I been missing out on £23.63 a week for the last 3 years ? That would be £94 a month which would help me out massively as I don't get PIP or any other benefit. It says there shouldn't be any trigger for a new assessment by changing. Problem is, what do I lose ? Is UC better in any other way ? I am very nervous as I am already 10 months over when my next assessment was meant to be.