planning

[DDAY JUNE 6]

If you have a problem with planning permission and nobody complains for over 4 years can planning force you to alter this

[buildersmate]

OK, the rules of the game are this:
If you build an extension to your dwelling that needed planning permission but you get it built and it remains for at least 4 years, Development Control (the Planning Permission people at the council) cannot then force you to demolish it. However you may still have a problem when it comes to selling the dwelling. After 4 years are up, you can apply for a Certificate of Lawfulness. This requires the same drawings as you would have needed for PP in the first place and you pay the same fee, but Development Control cannot refuse the certificate. That legalises the extension.
Note that the above only applies to a MODIFICATION to an existing use - if, say, you had an agricultural barn and you converted it to live in you would have to wait 10 YEARS (not 4) before you could consider yourself in the clear. This is because a Change of Use has occurred - from agricultural to dwelling-house.

[bushbaby_de]

buildermate's answer is not completely correct. Firstly to get a lawful development certificate you will have to supply proof that the structure or use has existed for the requisite period of time. This is 4 years for operational development or a change of use to a dwelling house or 10 years for any other change of use or breach of condition - therefore the example given above is slightly misleading. Perhaps if you give us more information on the scenario we can advise you further.