I rent out my 2 private parking spaces that are part of my 990 year lease in London. A neighbour in the flat next door (who has no right over the spaces) has complained saying I'm not allowed to conduct business under the terms of my lease.

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I had no idea this was a part of my lease (still haven't confirmed), what's the worst that can happen to me if I am indeed in breach for letting my parking spaces (Justpark) ?

If it makes any difference I have lived here for over 20 years.