You may not be allowed to race until you have gone through some sort of introduction to a 250M track. That's how it is at the three 250M tracks here in the U.S.
I would plan on getting some time on a 250M before your event, whether Manchester has such a rule or not. The transition won't be difficult. But you don't want it to be in a race situation.
Every track is different...even if they are the same length! The subtleties of angles and transitions make a big difference at race pace. It will be evident when you can't hold your line when entering and exiting turns.