According to Sky News:

The Archbishop of Canterbury said it was "clear" he had to quit after a damning review into the Church of England's handling of a sexual abuse scandal.

Speaking publicly for the first time since resigning almost a month ago, Justin Welby addressed the House of Lords saying he acknowledged the situation "required a head to roll".

The Archbishop is now in deeper trouble after it emerged that 'head-rolling' is a deviant sexual technique practised by men on uncircumcised boys.

A spokesperson explained:

Head-rolling has nothing whatever to do with the 'Shanghai Grip' made famous by Wallis Simpson as the means to give the Duke of Windsor a right royal rollicking.

His eminence was simply referring to the fact that someone had to take the fall for sexual misconduct in the church and it might as well be him.