I too am fairly new to the forum (4-5 months)
but in that time i have gained a wealth on info on these matter, but i still to ask for assitance.
I understand that there is a 7 year period BUT
Last month I was talking to an OC (manager) and he told me that it was there policy that they would only report for one year!!!!!!!!!! meaning if you were to dispute it the CA would not verify it.
Also i have a very bad loan with HSBC two years ago and in recent months i have disputed with all three CRA and they have deleted it.
It seems that some company's have an insider policy on how they deal with these issues.
If it is a bad trade line i would not hesitate to Dispute it as "not mine"
If that doesn't work you can GW.
Best Wishes