Thanks rnr, I've had a look at that but IG markets say they use IT-Finance charting for their advanced charting package.
IT-Finance do provide the advanced charting package to IG Markets and IT use ProRealTime although they don't advertise the fact on their website.
Have a look at their comparison of trading platforms and under Advanced features you see this reference "Automatic trend analysis: ProRealTrend draws support & resistance"
You can request a copy of the User Manual and Programming Guide from IT-Finance so that you can do some advance reading prior to setting up your account with IG.