Something to consider - I don't have an answer for it but I would be concerned about it if I were in similar situation...
In relation to the move to London, what happens if after a few months the company decides to let you go \ get rid of the role?
Will you be in a probationary period in the London role?
Will your service in Ireland count towards redundancy?
Will the redundancy be under UK law?
etc
No disrespect intended to AAM users, but I'd be surprised if anyone here would be able to answer questions like that so you might want to consider professional advice if you are seriously considering UK switch.