It's even worse if you click the logo on the 'Building Surveying' page!
Graham has the answer - if he he doesn't reply while I'm typing this, you need
<a href="../index.htm" target=top>
I think, or it may be
target="_top"
[Edit] This will open in the top-most frame, or Punky's
target = "_parent" will open in the parent frame - which may be the same.