In October 2008, Government changed the planning rules affecting house extensions and what you can and can't do to your house and its garden without planning permission. (Permitted Development)

The Government's new 'Interactive House' tool (click on each part for information) is a good starting point for checking whether you might need planning permission or not for your proposals:

The Government's Interactive House tool

As this is a complex area of planning law, you may still wish to e-mail MJM Planning for detailed advice and peace of mind.