Spitoon, sorry to say you are wrong with esters rising to the surface and when combined with water reduce friction. Not only did the AAIB not point at this the area called the 'patch' was filled with a regulating course not Marshall Asphalt which does suffer from this in the first months of operations.
The fact that there was a crosswind of biblical proportions and the rainfall rate would have caused standing water on any runway didn't figure very high in their report.
The fact that the runway wasn't grooved is irrelevant. Look at Bournemouth, Manchester, Humberside, Farnborough and CDG none of these runways are grooved.
Lastly, if you look at CAP 683 quoted previously you'll see that the certified friction carts have different figures. So if you need and can make use of a BA then surely you would need to ascertain the type of unit that was used to produce the unreliable figures?
SGC