In a nutshell:
If you stay outside regulated airspace you can go where you like without talking to anybody, flying on a see and be seen basis. (Careful, there are some restricted pieces of airspace too). With a few exceptions, as soon as you want to enter Regulated airspace you must obtain a clearance from the contrlling authority (even if you are flying Visual flight Rules).
If you wish to enter Manchester's airspace, even just to transit, you must call Manchetser Approach and ask for a transit clearance. Be prepared for a delay due to their increasingly busy IFR traffic, or a re-route out of their way. That applies to any airport busy enough to have its own regulated airspace.
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