Storage Built On Shared Access

[Lols]

Hi All, I asked 3 neighbours about building a storage area for hand gardening tools, soil, garden hose etc. All said yes. Now built (under 3 square mitres) and they have said no. I received a solicitors letter and sorted that as there is no legal implications as they say it is 'communal access' but all deeds and plans (I checked in planning) state 'shared access' for maintenance and repairs to buildings. I have not stopped access to the brickwall at the end and everyone can use it for garden stuff. I only have space for a few planters but 2 residents have raised gated patios! They have now complained to Planning and I have been asked to put in a retrospective application at a fee of £275! It is shared area and nothing to do with planning in my opinion it is a neighbour dispute or a legal matter as planning have no jurisdiction over 'shared' areas. Am I right?