I just found this it explains the 4year and 10year thing. I think you are OK at 4 years
Time limits
The Planning and Compensation Act 1991 introduced rolling time limits within which local planning authorities can take planning enforcement action against breaches of planning control.
The time limits are:
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four years for building, engineering, mining or other operations in, on, over or under land, without planning permission. This development becomes immune from enforcement action four years after the operations are substantially completed
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four years for the change of use of a building, or part of a building, to use as a single dwelling house. Enforcement action can no longer be taken once the unauthorised use has continued for four years without any enforcement action being taken
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10 years for all other development. The 10 year period runs from the date the breach of planning control was committed
Once these time limits have passed, the development becomes lawful, in terms of planning.
Information which must be provided with the application
Applications for Lawful Development Certificates should include the following information:
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whether the application relates to:
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a use
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a building operation
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a condition not complied with
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