I suspect the officers wouldn't have cared too much about policy, given the era and the situation. They'd have chosen the person with the highest chance of success, probably the smallest person with the best flying skills.
So, speaking German or French without a British accent likely would have been a pre, as would being familiar with the home town of your cover.
Also, they would be reluctant to let their top craftsmen go. If you were really good at falsifying passports or ID cards, for example, your skills would be useful to keep around for future escapes.