error on documented boundary

I have been looking into purchasing a slice of land next to my current boundary. This will be from the local council. As part of my investigation into who owned the land etc, i had obtained a copy of the title plan for my current property, on looking at this i have noticed that my outdoor garden room has been placed outside of the recorded boundary line for my property. The outdoor garden room was built on land that was inside my fence line, so i have not placed on other land outside of what is my fence line.

I feel the plans may have been a little rushed as there was a backlog of registries at the time i was remortgaging my house and titles had not been registered on the system and ended up being expedited for remortgage.

Where/who can i contact to update for this error, as do not want this to be a contentious issue in the future with people thinking i have taken land that is not mine.

Daniel - you should report an 'error' using our contact form 
Public guidance: dealing with land and property - GOV.UK

Thank you for this, do you advise that it is best to wait until i am purchasing the land and have the conveyancer/solicitor that will be helping with this to register the error at the same time of update of land transfer effectively changing my boundary?

Daniel - that's for you and your conveyancer to discuss/decide. If you are buying with a mortgage then the lender may have the actual say as to yes or no re completion and when the 'error' is corrected