In the not too distant past European bison were part of the British ecosystem. With the ability to browse trees and therefore to halt there expansion, and highly important ecosystem engineers in the same way that beavers are.
The plan is to initially release a male and two or three females into a small enclosures in Kent, however there is a bigger area into which people would be allowed to walk that they would be released into as their numbers increase. Furthermore the idea would be that over time as they reproduce bison would be reintroduced to other parts of the UK from this founding herd.
While bison are not predators this would be one of the bigger reintroductions to happen in the UK ever if it was allowed to proceed fully.
They would likely be highly beneficial to all sorts of areas of the UK, both in terms of their tourism and the the services they would offer to the local environment.
We will have to watch this space to see if this is actually allowed to go ahead fully.