When I asked which one I required, she said probably building notice but
wasnt sure. How can I tell ? There are no changes to the size of the
house,
no changes to sewers, drains or electricals.

Building notice, unless the house is listed, when things (as always) get far
more complicated.

The building notice comes in two forms. You can either just tell them that
you're doing it and they come round to have a look to make sure it's all up
to scratch. Or you can submit plans, showing all the calculations.

Christian.