Approximately 39,200 retrospective planning applications have been filed for developments either started or completed in the past three years, Churchill Home Insurance has found.
Home extensions are the most popular reasons for seeking retrospective planning permission.
Pritpal Powar, head of Churchill Home Insurance, said: “Homeowners are increasingly choosing to expand their current homes to accommodate growing family sizes, rather than move to a new house.
“However, before beginning any development, we encourage people to check whether they need planning permission and if they do, to wait until this has been granted before starting work.
“It is also important for householders to advise their insurance provider on any works they are planning, to ensure they have the correct cover in place for their property.
“Whilst any major household development is likely to come with a certain amount of upheaval, we hope that by taking these steps homeowners should ensure that they aren’t subjected to any unnecessary stress during the process.”
In the past three years, the most commonly reported reasons for applying for retrospective planning permission were single-floor extensions (2,218 applications), double-floor extensions (459) and loft conversions (424).
This was followed by garage conversions (309) and open-plan spaces (106).
One in eight planning applications are rejected by local authorities.
The most common reasons for authorities rejecting applications include the development being out of character (28%), loss of privacy (10%) or overdevelopment (5%).
On a regional level, Scotland had the highest number of retrospective planning applications, accounting for 20% (7,949) of all applications over the past three years.
This was followed by London (5,612) and the South East (5,372), both receiving 14% of the UK’s retrospective planning applications.
Wales had the highest refusal rate with more than a quarter (28%) of retrospective planning applications refused.
Around a fifth of applications were denied in both London (21%) and Scotland (18%).