Allow me to clarify my hypothetical example -
It's a particular day. BP equities open on the LSE at 4.10. I am already long with IG. I have a stop set with IG at 4.00. At the end of the day I am surprised to see that on the LSE, BP equities have a high of 4.15 and a low of 4.05 however my stop with IG has been hit at 4.00. This is the scenario which both myself and friends have encountered.
I phone IG to question them to which which they respend that I'm actually trading IG's market-made market (which lowed at say 3.99) not the underlying BP equities market (which lowed at 4.05) and hence that is fine (with them).
I'm well aware that it required a very big trade to move the market, expecially for BP!
Stop Hunting does happen unfortunately.