A 'frozen' ATPL is a marketing term/shorthand for holding a UK (or JAR?) CPL + IR + ATPL exam passes. It means that you can apply for the issue of an ATPL once you've gained the required experience. An MCC is not specifically required **however** it has become difficult (but not impossible) to obtain the necessary experience without also having done an MCC due to the multi-crew experience requirements combined with initial type rating requirements.