The EAT has handed down judgment in the important case of TGWU v Safeway Stores. It is authority for the proposition that it will almost always be permissible to amend a Claim Form to introduce a new legal cause of action which relies on already pleaded facts, even if the new cause of action is out of time (see paras. 13 and 15).
Even if you don't have a case involving this particular point, this is a decision well worth reading for Underhill J.'s analysis and explanation of the authorities on amending Claim Forms.