Thanks for checking this out, UK contingent!
A couple of things to remember:
1) These tests are conducted using a traditional American non water-heating frontloader. Your bio detergents may be formulated for profile washes, which allow a detergent to remove certain stains in warm water, then heating to a high temp to remove stains that respond better to very hot water.
2) Most UK washers have a much longer cycle than my machine. Total cycle time for me is 55 minutes (including an 11-minute final spin). Seems to me most of your machines have longer wash cycles (18-minutes is the longest wash on the Frigidaire).
3) I have mechanically-softened water. It is slippery even without adding detergent.
4) This is a very difficult test. I stained the towels heavily, then hung them to dry overnight.
I think both detergents are top-shelf; In my test, Persil took the checkered flag. Its rinsing ability is impressive, too.