The discretion of a tribunal to regulate its procedure includes a discretion to grant leave for amendment of a claim and/or response (r. 10(2)(q) of the 2004 rules of procedure - see Procedure of Employment Tribunals/2004 rules/rule 10 - general power to manage proceedings ).
In practice the discretion is usually exercised on application to a chairman alone prior to the substantive hearing by the tribunal.
For note on the separate question of bringing up new points on appeal to the EAT go to Employment Appeal Tribunal/a general note .
See also notes at: