Do I need approval to make internal alterations within my house?

Yes
If the alterations are of a structural nature (eg the removal or part removal of a load bearing wall, or a chimney) or affect the means of escape in the event of fire

Generally, if the alteration involves the insertion of a beam or lintel or will affect the stability of the building then the alteration is a structural one

Alterations that may affect the fire escape of a dwelling include the erection or removal of an internal wall (including non-loadbearing walls), alterations to the stairs, the removal of doors, etc

Please note; replacing existing windows can also affect means of escape, unless the new window is no worse or better than the existing, with respect to its opening size, position and availability

In addition to the above, the installation or alteration of bathroom and kitchen appliances involving drainage work is required also requires approval