The following chart plots the average performance of the FTSE 100 Index during July since 1984 (more info on this type of chart).
The chart shows that on average, the market rises for the first week of July, then drifts lower for the following two weeks, but ends strongly in the final week.
The average chart for June was posted a month ago here. The following reproduces that chart and overlays the actual FTSE 100 for June 2013.
In an average June the market is weak; this was true also in 2013, but the market was much weaker than in an average year.