Not only is it bad enough when as an employer you get an Employment Tribunal Claim, but now it would seem that you can never be too sure as to the extent of that claim. In the case of TGWU v Safeway Stores the Employment Appeal Tribunal gave authority for the notion that it will almost always be permissable to amend a Claim to introduce a new legal cause of action. This is where the new legal action relies on already pleaded facts (in the Claim Form) even if that new cause of action is out of time. You can read the case here.
As an employer it would be prudent to carefully review any Claim Forms you receive to ascertain whether there are any facts which may give rise to additional legal causes of action just so you do not get caught out.