Might be a bit late: from the CAA website - All certifying staff must hold a Part-66 licence by 28 September 2008. In order to continue certifyng aircraft above 5700kg engineers must have converted to a Part-66 by 28 September 2006.
This may of been extended, but as your licence has expired by more than a year you might well find you are too late for conversion, best thing is to call the CAA. Where have you been?