When LGW resurfaced the main last year, this same debacle dragged on for a number of weeks. It wasn't long before NATS & BAA became quite well informed of every airlines SOP's and eventually found a solution.
I recall the turning point was when a B744 tried to turn off and just kept on slidin'!!
Perhaps BAA LL & ATC ops should give Sussex Regional a call.
As far as grip tester runs went, BAA refused several requests, and even when they did do them, the equipments calibration wasn't exact enough to pass to pilots?!!
Ta ta,
PA