Ummm..... If you are the guy getting blown, then you are the person receiving the oral sex!
Once again I mis-speak myself. Man you guys are on the ball!
What I meant was the person receiving the bodily fluids! It is the exchange of (certain) bodily fluids that causes the spread of HIV. CIM is therefore risky for the receiver of the bodily fluids mostly if they have open sores/cuts to the mouth/gums.
There are no recorded cases of HIV spreading from saliva so even if you have an open wound on your cock the risk appears to also be nil. Of course, just because there are no recorded cases doesn't mean it hasn't happened so probably best not to cut your dick just to experiment.
The incidence of HIV in the UK is around 0.15% of the population which is pretty tiny but for sure unprotected sex of any kind will raise your risk; for punters the biggest risk is actually RO with a WG who allows CIM but again you would have to have an open cut/sore on your mouth/gums.
So two options to reduce your risk:
1) Don't floss on the morning of a punt, brush your teeth a good 3-4 hours before and use mints/gum to freshen your mouth rather than a toothbrush.
2) Switch to a WG who only does OW.
3) Don't do RO.
Again, you pay your money you take your choice, only "no risk" sex is "no sex" yadayadayada.