Most successful single release week?

First it was Shayne Ward, then Rihanna and now Infernal. That's 3 records debuting the same week and all reaching #2 in the singles chart, which got me thinking.

I wonder what one week of releases ever produced the most number one singles? Occasionally, we get 2 singles released the same week and they swap places at the top of the chart on their second week. But I wouldn't be surprised if there have been instances where 3 or more records have gone on to reach number 1 (i.e. from same day release).