Interesting ... never heard of anybody calling up Northolt. Do they offer a RIS? If so that would be useful.
Tell you what you could do to make some work, ATCO17: lobby the CAA to introduce one of the greatest contributions to safety in that area: a GPS approach into Elstree, Panshanger, etc, and you can then do the radar service for it, free of charge since they won't be able to afford to pay for it anyway. This is only partly tongue in cheek, because the matter will have to come to a head if GPS approaches ever take off (so to speak) - because, on the scale of GA utility in the UK as a whole, they are largely pointless unless provided at non-ATC airfields.