Heathrow had about 30% of the traffic in the UK in 2011. Given that they apply minimum wake turbulence spacing between a far, far higher proportion of their traffic than any other UK airport, nowhere else even comes close, 65% sounds doesn't sound excessive at all to me.
I don't have the figures, but I wouldn't be remotely surprised if, per traffic pair at minimum spacing, they actually had a better safety record than anywhere else since they practice it so much.