From what I understand, the vast majority of Kagyu teachers and groups follow Ogyen Trinley Dorje. However the group local to me, dechen.org, follows Trinley Thaye Dorje. The lama in question is Jampa Thaye and, by all accounts that I've read, he seems to be very legitimate and reputable. I haven't come across any criticisms of his teachings or ethics.
He is from everything I hear too.
But if I study with this group, does this mean that I am not allowed to take other teachings from lamas who follow Ogyen Trinley Dorje? ie will I be isolating myself from the rest of Kagyu Buddhism? Or is it accepted to take teachings from teachers on both sides of the dividing line as long as they are legitimate teachers?
I don't think you would be turned away by any Karma Kagyu teacher. I think actually this is a question for you to ask Jampa Thaye rather than an internet forum. If he sees no problem in you getting teachings from lamas who support Urgyen Trinley Dorje then you are good to go. If he doesn't think it's a good idea for whatever reason then it's up to you to decide to follow his advice or look elsewhere if that is what you think is the right thing to do.
No matter what tradition you are in, it is always a good idea to look around different sanghas and teachers to get a feel for what is out there at the start. In the North of England you are (relatively) close to the huge monastery at Samye Ling in southern Scotland, Karma Ling in Birmingham, Lama Rabsang's centre in Brynmawr in Wales, Thrangu House in Oxford, Marpa House nr Cambridge. And many other non-Karma Kagyu centres.
However, if you like Jampa Thaye's style and find his centre's welcoming and convenient for regular practice then I would not let the Karmapa controversy dissuade you. Possibly down the line, when taking higher empowerments and doing guru yoga etc., it might be more of an issue but hopefully by that time you will know yourself which path you want to take.