You are right Royston!
I did miss that it said "in London" on the next line.
Sorry. A mistake.(If it was a lie I would hardly have provided a link to it would I?)
Remember, you gave a figure of 4%, so you were wrong too.
So, replace 8.5% with 5.6%, and everything else I said still stands.
Over a third are over 44, and that is just the survivors!

It also says
"There has been a large rise in newly diagnosed HIV infections among MSM each year since the turn of the century. In 2007 there were a total of 2,679 newly diagnosed HIV infections (increasing to 3160 if adjusted for missing data), representing an increase of 8% since 2006, and 74% since 2000"
(The increase for heteros, remember was infinitesimal and only due to immigration anyway.)

The 3% I mentioned was the proportion of MSMs in the population.
The quote I provided gave the figures for ghon.