Engine 850: B5252S/2.4/10v: Missfire/plug leads

[LPGjonderby]

Having just fitted a new cap and rotor arm, both by scantech. My S70 auto still has the same missfire !!

The cap & rotor are exactly the same make & type as the ones that have come off. Could it be Scantech stuff is crap ?
Having spoken with Volvopartsonline, they say they sell a dozen or so of these each week and never have them returned under warranty. So am thinking they are fine, unless you guys no otherwise.
The coil and lead are new.
The ignition leads were replaced around 2,500 miles ago when Victor had his original replacement cap & rotor.
These appear to be of a poor quality compared to the pictures of the OEM ones and others that are available.
Does anyone have experience of there car missfiring when cheaper leads have been fitted. Am about to order a new set from fastlane autos. However will this be the root problem.
Having had a timing light on the job, all the leads are missing in the same way at will as and when they fancy.
Should I just go the whole hog and order a Bosch cap and arm ? Although am told by Volvopartsonline the ones I have bought are good items, or do I just order some better quality leads.

Any experience or ideas would be welcomed.

Many thanks

Jon